Commit 31070f6c authored by Chirantan Ekbote's avatar Chirantan Ekbote Committed by Miklos Szeredi

fuse: Fix parameter for FS_IOC_{GET,SET}FLAGS

The ioctl encoding for this parameter is a long but the documentation says
it should be an int and the kernel drivers expect it to be an int.  If the
fuse driver treats this as a long it might end up scribbling over the stack
of a userspace process that only allocated enough space for an int.

This was previously discussed in [1] and a patch for fuse was proposed in
[2].  From what I can tell the patch in [2] was nacked in favor of adding
new, "fixed" ioctls and using those from userspace.  However there is still
no "fixed" version of these ioctls and the fact is that it's sometimes
infeasible to change all userspace to use the new one.

Handling the ioctls specially in the fuse driver seems like the most
pragmatic way for fuse servers to support them without causing crashes in
userspace applications that call them.

[1]: https://lore.kernel.org/linux-fsdevel/20131126200559.GH20559@hall.aurel32.net/T/
[2]: https://sourceforge.net/p/fuse/mailman/message/31771759/Signed-off-by: default avatarChirantan Ekbote <chirantan@chromium.org>
Fixes: 59efec7b ("fuse: implement ioctl support")
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
parent 7779b047
...@@ -18,6 +18,7 @@ ...@@ -18,6 +18,7 @@
#include <linux/swap.h> #include <linux/swap.h>
#include <linux/falloc.h> #include <linux/falloc.h>
#include <linux/uio.h> #include <linux/uio.h>
#include <linux/fs.h>
static struct page **fuse_pages_alloc(unsigned int npages, gfp_t flags, static struct page **fuse_pages_alloc(unsigned int npages, gfp_t flags,
struct fuse_page_desc **desc) struct fuse_page_desc **desc)
...@@ -2775,7 +2776,16 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg, ...@@ -2775,7 +2776,16 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
struct iovec *iov = iov_page; struct iovec *iov = iov_page;
iov->iov_base = (void __user *)arg; iov->iov_base = (void __user *)arg;
switch (cmd) {
case FS_IOC_GETFLAGS:
case FS_IOC_SETFLAGS:
iov->iov_len = sizeof(int);
break;
default:
iov->iov_len = _IOC_SIZE(cmd); iov->iov_len = _IOC_SIZE(cmd);
break;
}
if (_IOC_DIR(cmd) & _IOC_WRITE) { if (_IOC_DIR(cmd) & _IOC_WRITE) {
in_iov = iov; in_iov = iov;
......
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