- 29 Jul, 2012 20 commits
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Kees Cook authored
This adds symlink and hardlink restrictions to the Linux VFS. Symlinks: A long-standing class of security issues is the symlink-based time-of-check-time-of-use race, most commonly seen in world-writable directories like /tmp. The common method of exploitation of this flaw is to cross privilege boundaries when following a given symlink (i.e. a root process follows a symlink belonging to another user). For a likely incomplete list of hundreds of examples across the years, please see: http://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=/tmp The solution is to permit symlinks to only be followed when outside a sticky world-writable directory, or when the uid of the symlink and follower match, or when the directory owner matches the symlink's owner. Some pointers to the history of earlier discussion that I could find: 1996 Aug, Zygo Blaxell http://marc.info/?l=bugtraq&m=87602167419830&w=2 1996 Oct, Andrew Tridgell http://lkml.indiana.edu/hypermail/linux/kernel/9610.2/0086.html 1997 Dec, Albert D Cahalan http://lkml.org/lkml/1997/12/16/4 2005 Feb, Lorenzo Hernández García-Hierro http://lkml.indiana.edu/hypermail/linux/kernel/0502.0/1896.html 2010 May, Kees Cook https://lkml.org/lkml/2010/5/30/144 Past objections and rebuttals could be summarized as: - Violates POSIX. - POSIX didn't consider this situation and it's not useful to follow a broken specification at the cost of security. - Might break unknown applications that use this feature. - Applications that break because of the change are easy to spot and fix. Applications that are vulnerable to symlink ToCToU by not having the change aren't. Additionally, no applications have yet been found that rely on this behavior. - Applications should just use mkstemp() or O_CREATE|O_EXCL. - True, but applications are not perfect, and new software is written all the time that makes these mistakes; blocking this flaw at the kernel is a single solution to the entire class of vulnerability. - This should live in the core VFS. - This should live in an LSM. (https://lkml.org/lkml/2010/5/31/135) - This should live in an LSM. - This should live in the core VFS. (https://lkml.org/lkml/2010/8/2/188) Hardlinks: On systems that have user-writable directories on the same partition as system files, a long-standing class of security issues is the hardlink-based time-of-check-time-of-use race, most commonly seen in world-writable directories like /tmp. The common method of exploitation of this flaw is to cross privilege boundaries when following a given hardlink (i.e. a root process follows a hardlink created by another user). Additionally, an issue exists where users can "pin" a potentially vulnerable setuid/setgid file so that an administrator will not actually upgrade a system fully. The solution is to permit hardlinks to only be created when the user is already the existing file's owner, or if they already have read/write access to the existing file. Many Linux users are surprised when they learn they can link to files they have no access to, so this change appears to follow the doctrine of "least surprise". Additionally, this change does not violate POSIX, which states "the implementation may require that the calling process has permission to access the existing file"[1]. This change is known to break some implementations of the "at" daemon, though the version used by Fedora and Ubuntu has been fixed[2] for a while. Otherwise, the change has been undisruptive while in use in Ubuntu for the last 1.5 years. [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/linkat.html [2] http://anonscm.debian.org/gitweb/?p=collab-maint/at.git;a=commitdiff;h=f4114656c3a6c6f6070e315ffdf940a49eda3279 This patch is based on the patches in Openwall and grsecurity, along with suggestions from Al Viro. I have added a sysctl to enable the protected behavior, and documentation. Signed-off-by:
Kees Cook <keescook@chromium.org> Acked-by:
Ingo Molnar <mingo@elte.hu> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Al Viro <viro@zeniv.linux.org.uk>
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Jeff Layton authored
I can reliably reproduce the following panic by simply setting an audit rule on a recent 3.5.0+ kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000040 IP: [<ffffffff810d1250>] audit_copy_inode+0x10/0x90 PGD 7acd9067 PUD 7b8fb067 PMD 0 Oops: 0000 [#86] SMP Modules linked in: nfs nfs_acl auth_rpcgss fscache lockd sunrpc tpm_bios btrfs zlib_deflate libcrc32c kvm_amd kvm joydev virtio_net pcspkr i2c_piix4 floppy virtio_balloon microcode virtio_blk cirrus drm_kms_helper ttm drm i2c_core [last unloaded: scsi_wait_scan] CPU 0 Pid: 1286, comm: abrt-dump-oops Tainted: G D 3.5.0+ #1 Bochs Bochs RIP: 0010:[<ffffffff810d1250>] [<ffffffff810d1250>] audit_copy_inode+0x10/0x90 RSP: 0018:ffff88007aebfc38 EFLAGS: 00010282 RAX: 0000000000000000 RBX: ffff88003692d860 RCX: 00000000000038c4 RDX: 0000000000000000 RSI: ffff88006baf5d80 RDI: ffff88003692d860 RBP: ffff88007aebfc68 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000 R13: ffff880036d30f00 R14: ffff88006baf5d80 R15: ffff88003692d800 FS: 00007f7562634740(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000040 CR3: 000000003643d000 CR4: 00000000000006f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process abrt-dump-oops (pid: 1286, threadinfo ffff88007aebe000, task ffff880079614530) Stack: ffff88007aebfdf8 ffff88007aebff28 ffff88007aebfc98 ffffffff81211358 ffff88003692d860 0000000000000000 ffff88007aebfcc8 ffffffff810d4968 ffff88007aebfcc8 ffff8800000038c4 0000000000000000 0000000000000000 Call Trace: [<ffffffff81211358>] ? ext4_lookup+0xe8/0x160 [<ffffffff810d4968>] __audit_inode+0x118/0x2d0 [<ffffffff811955a9>] do_last+0x999/0xe80 [<ffffffff81191fe8>] ? inode_permission+0x18/0x50 [<ffffffff81171efa>] ? kmem_cache_alloc_trace+0x11a/0x130 [<ffffffff81195b4a>] path_openat+0xba/0x420 [<ffffffff81196111>] do_filp_open+0x41/0xa0 [<ffffffff811a24bd>] ? alloc_fd+0x4d/0x120 [<ffffffff811855cd>] do_sys_open+0xed/0x1c0 [<ffffffff810d40cc>] ? __audit_syscall_entry+0xcc/0x300 [<ffffffff811856c1>] sys_open+0x21/0x30 [<ffffffff81611ca9>] system_call_fastpath+0x16/0x1b RSP <ffff88007aebfc38> CR2: 0000000000000040 The problem is that do_last is passing a negative dentry to audit_inode. The comments on lookup_open note that it can pass back a negative dentry if O_CREAT is not set. This patch fixes the oops, but I'm not clear on whether there's a better approach. Cc: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by:
Jeff Layton <jlayton@redhat.com> Signed-off-by:
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Al Viro authored
... only needed if it's been in descriptor table Signed-off-by: -
Al Viro authored
Signed-off-by: -
Al Viro authored
sigh... * opened files have non-NULL dentries and non-NULL inodes * close_filp() needs current->files only if the file had been in descriptor table. Signed-off-by: -
Al Viro authored
* filp_close() needs non-NULL second argument only if it'd been in descriptor table * opened files have non-NULL dentries, TYVM * ... and those dentries are positive - it's kinda hard to open a file that doesn't exist. Signed-off-by: -
Al Viro authored
a) vfs_llseek() does *not* access userland pointers of any kind b) neither does filp_close(), for that matter c) ... nor filp_open() d) vfs_read() does, but we do have a wrapper for that (kernel_read()), so there's no need to reinvent it. e) passing current->files to filp_close() on something that never had been in descriptor table is pointless. ISAGN: voodoo dolls to be used on voodoo programmers... Signed-off-by: -
Al Viro authored
Signed-off-by: -
Al Viro authored
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Al Viro authored
What inline? Its only use is passing its address to call_rcu(), for fuck sake! Signed-off-by: -
Al Viro authored
less work on failure that way Signed-off-by: -
Al Viro authored
* ->lookup() never gets hit with . or .. * dentry it gets is unhashed, so unless we had gone and hashed it ourselves, there's no need to d_drop() the sucker. * wrong name printed in one of the printks (NULL, in fact) Signed-off-by: -
Al Viro authored
Signed-off-by: -
Al Viro authored
One side effect - attempt to create a cross-device link on a read-only fs fails with EROFS instead of EXDEV now. Makes more sense, POSIX allows, etc. Signed-off-by: -
Al Viro authored
Note that applying umask can't affect their results. While that affects errno in cases like mknod("/no_such_directory/a", 030000) yielding -EINVAL (due to impossible mode_t) instead of -ENOENT (due to inexistent directory), IMO that makes a lot more sense, POSIX allows to return either and any software that relies on getting -ENOENT instead of -EINVAL in that case deserves everything it gets. Signed-off-by: -
Al Viro authored
releases what needs to be released after {kern,user}_path_create() Signed-off-by: -
Al Viro authored
... and cleaning spufs_create() a bit, while we are at it Signed-off-by: -
Al Viro authored
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Al Viro authored
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Al Viro authored
now that __fput() is *not* done in any callchain containing mmput(), we can do that... Signed-off-by:
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- 22 Jul, 2012 20 commits
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Al Viro authored
Signed-off-by: -
Al Viro authored
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Al Viro authored
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Al Viro authored
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Al Viro authored
all we need it for is file->private_data, which is assign-once, already assigned by that point and, incidentally, its value is already in use by zoran ->mmap() anyway. So just store that pointer instead... Signed-off-by: -
Al Viro authored
... and keep the sodding requests on stack - they are small enough. Signed-off-by: -
Al Viro authored
d_instantiate(dentry, inode); unlock_new_inode(inode); is a bad idea; do it the other way round... Signed-off-by: -
Al Viro authored
locking/unlocking for rcu walk taken to a couple of inline helpers Signed-off-by: -
Al Viro authored
really convoluted test in there has grown up during struct mount introduction; what it checks is that we'd reached the root of mount tree.
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Eric Sandeen authored
Use the new custom EOF argument to generic_file_llseek_size so that SEEK_END will go to the max hash value for htree dirs in ext3 rather than to i_size_read() Signed-off-by:
Eric Sandeen <sandeen@redhat.com> Signed-off-by:
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Eric Sandeen authored
Use the new functionality in generic_file_llseek_size() to accept a custom EOF position, and un-cut-and-paste all the vfs llseek code from ext4. Also fix up comments on ext4_llseek() to reflect reality. Signed-off-by:
Eric Sandeen <sandeen@redaht.com> Signed-off-by:
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Eric Sandeen authored
For ext3/4 htree directories, using the vfs llseek function with SEEK_END goes to i_size like for any other file, but in reality we want the maximum possible hash value. Recent changes in ext4 have cut & pasted generic_file_llseek() back into fs/ext4/dir.c, but replicating this core code seems like a bad idea, especially since the copy has already diverged from the vfs. This patch updates generic_file_llseek_size to accept both a custom maximum offset, and a custom EOF position. With this in place, ext4_dir_llseek can pass in the appropriate maximum hash position for both maxsize and eof, and get what it wants. As far as I know, this does not fix any bugs - nfs in the kernel doesn't use SEEK_END, and I don't know of any user who does. But some ext4 folks seem keen on doing the right thing here, and I can't really argue. (Patch also fixes up some comments slightly) Signed-off-by:
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Jan Kara authored
wakeup_flusher_threads(0) will queue work doing complete writeback for each flusher thread. Thus there is not much point in submitting another work doing full inode WB_SYNC_NONE writeback by writeback_inodes_sb(). After this change it does not make sense to call nonblocking ->sync_fs and block device flush before calling sync_inodes_sb() because wakeup_flusher_threads() is completely asynchronous and thus these functions would be called in parallel with inode writeback running which will effectively void any work they do. So we move sync_inodes_sb() call before these two functions. Signed-off-by:
Jan Kara <jack@suse.cz> Signed-off-by:
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Jan Kara authored
It is not necessary to write block devices twice. The reason why we first did flush and then proper sync is that for_each_bdev() { write_bdev() wait_for_completion() } is much slower than for_each_bdev() write_bdev() for_each_bdev() wait_for_completion() when there is bigger amount of data. But as is seen in the above, there's no real need to scan pages and submit them twice. We just need to separate the submission and waiting part. This patch does that. Signed-off-by: -
Jan Kara authored
In case block device does not have filesystem mounted on it, sys_sync will just ignore it and doesn't writeout its dirty pages. This is because writeback code avoids writing inodes from superblock without backing device and blockdev_superblock is such a superblock. Since it's unexpected that sync doesn't writeout dirty data for block devices be nice to users and change the behavior to do so. So now we iterate over all block devices on blockdev_super instead of iterating over all superblocks when syncing block devices. Reviewed-by:
Christoph Hellwig <hch@lst.de> Signed-off-by:
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Jan Kara authored
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Jan Kara authored
Change the order of operations during sync from for_each_sb { writeback_inodes_sb(); sync_fs(nowait); __sync_blockdev(nowait); } for_each_sb { sync_inodes_sb(); sync_fs(wait); __sync_blockdev(wait); } to for_each_sb writeback_inodes_sb(); for_each_sb sync_fs(nowait); for_each_sb __sync_blockdev(nowait); for_each_sb sync_inodes_sb(); for_each_sb sync_fs(wait); for_each_sb __sync_blockdev(wait); This is a preparation for the following patches in this series. Reviewed-by: -
Jan Kara authored
Since the moment writes to quota files are using block device page cache and space for quota structures is reserved at the moment they are first accessed we have no reason to sync quota before inode writeback. In fact this order is now only harmful since quota information can easily change during inode writeback (either because conversion of delayed-allocated extents or simply because of allocation of new blocks for simple filesystems not using page_mkwrite). So move syncing of quota information after writeback of inodes into ->sync_fs method. This way we do not have to use ->quota_sync callback which is primarily intended for use by quotactl syscall anyway and we get rid of calling ->sync_fs() twice unnecessarily. We skip quota syncing for OCFS2 since it does proper quota journalling in all cases (unlike ext3, ext4, and reiserfs which also support legacy non-journalled quotas) and thus there are no dirty quota structures. CC: "Theodore Ts'o" <tytso@mit.edu> CC: Joel Becker <jlbec@evilplan.org> CC: reiserfs-devel@vger.kernel.org Acked-by:
Steven Whitehouse <swhiteho@redhat.com> Acked-by:
Dave Kleikamp <shaggy@kernel.org> Reviewed-by:
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Jan Kara authored
Split off part of dquot_quota_sync() which writes dquots into a quota file to a separate function. In the next patch we will use the function from filesystems and we do not want to abuse ->quota_sync quotactl callback more than necessary. Acked-by:
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Jan Kara authored
In principle, a filesystem may want to have ->sync_fs() called during sync(1) although it does not have a bdi (i.e. s_bdi is set to noop_backing_dev_info). Only writeback code really needs bdi set to something reasonable. So move the checks where they are more logical. Reviewed-by:
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