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authorMiklos Szeredi <mszeredi@suse.cz>2008-05-01 04:34:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-05-01 08:03:59 -0700
commit02c6be615f1fcd37ac5ed93a3ad6692ad8991cd9 (patch)
tree9c5047ed8b165a3388d5c61b2702f7cc12954766 /fs/utimes.c
parent2850699c59d513a0cd0c68f60f75609a5f9d4d32 (diff)
downloadlwn-02c6be615f1fcd37ac5ed93a3ad6692ad8991cd9.tar.gz
lwn-02c6be615f1fcd37ac5ed93a3ad6692ad8991cd9.zip
vfs: fix permission checking in sys_utimensat
If utimensat() is called with both times set to UTIME_NOW or one of them to UTIME_NOW and the other to UTIME_OMIT, then it will update the file time without any permission checking. I don't think this can be used for anything other than a local DoS, but could be quite bewildering at that (e.g. "Why was that large source tree rebuilt when I didn't modify anything???") This affects all kernels from 2.6.22, when the utimensat() syscall was introduced. Fix by doing the same permission checking as for the "times == NULL" case. Thanks to Michael Kerrisk, whose utimensat-non-conformances-and-fixes.patch in -mm also fixes this (and breaks other stuff), only he didn't realize the security implications of this bug. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Cc: Ulrich Drepper <drepper@redhat.com> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/utimes.c')
-rw-r--r--fs/utimes.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/fs/utimes.c b/fs/utimes.c
index a2bef77dc9c9..af059d5cb485 100644
--- a/fs/utimes.c
+++ b/fs/utimes.c
@@ -40,9 +40,14 @@ asmlinkage long sys_utime(char __user *filename, struct utimbuf __user *times)
#endif
+static bool nsec_special(long nsec)
+{
+ return nsec == UTIME_OMIT || nsec == UTIME_NOW;
+}
+
static bool nsec_valid(long nsec)
{
- if (nsec == UTIME_OMIT || nsec == UTIME_NOW)
+ if (nsec_special(nsec))
return true;
return nsec >= 0 && nsec <= 999999999;
@@ -119,7 +124,15 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags
newattrs.ia_mtime.tv_nsec = times[1].tv_nsec;
newattrs.ia_valid |= ATTR_MTIME_SET;
}
- } else {
+ }
+
+ /*
+ * If times is NULL or both times are either UTIME_OMIT or
+ * UTIME_NOW, then need to check permissions, because
+ * inode_change_ok() won't do it.
+ */
+ if (!times || (nsec_special(times[0].tv_nsec) &&
+ nsec_special(times[1].tv_nsec))) {
error = -EACCES;
if (IS_IMMUTABLE(inode))
goto mnt_drop_write_and_out;