From 02c6be615f1fcd37ac5ed93a3ad6692ad8991cd9 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Thu, 1 May 2008 04:34:45 -0700 Subject: [PATCH] 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 Cc: Ulrich Drepper Cc: Michael Kerrisk Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/utimes.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/fs/utimes.c b/fs/utimes.c index a2bef77..af059d5 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; -- 1.8.2.3