• Patrick Palka's avatar
    kernel/printk/printk.c: fix faulty logic in the case of recursive printk · 000a7d66
    Patrick Palka authored
    We shouldn't set text_len in the code path that detects printk recursion
    because text_len corresponds to the length of the string inside textbuf.
    A few lines down from the line
    
        text_len = strlen(recursion_msg);
    
    is the line
    
        text_len += vscnprintf(text + text_len, ...);
    
    So if printk detects recursion, it sets text_len to 29 (the length of
    recursion_msg) and logs an error.  Then the message supplied by the
    caller of printk is stored inside textbuf but offset by 29 bytes.  This
    means that the output of the recursive call to printk will contain 29
    bytes of garbage in front of it.
    
    This defect is caused by commit 458df9fd ("printk: remove separate
    printk_sched buffers and use printk buf instead") which turned the line
    
        text_len = vscnprintf(text, ...);
    
    into
    
        text_len += vscnprintf(text + text_len, ...);
    
    To fix this, this patch avoids setting text_len when logging the printk
    recursion error.  This patch also marks unlikely() the branch leading up
    to this code.
    
    Fixes: 458df9fd ("printk: remove separate printk_sched buffers and use printk buf instead")
    Signed-off-by: default avatarPatrick Palka <patrick@parcs.ath.cx>
    Reviewed-by: default avatarPetr Mladek <pmladek@suse.cz>
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    000a7d66
printk.c 76.1 KB