The patch titled Subject: tmpfs: fix use-after-free of mempolicy object has been removed from the -mm tree. Its filename was tmpfs-fix-use-after-free-of-mempolicy-object.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Greg Thelen <gthelen@xxxxxxxxxx> Subject: tmpfs: fix use-after-free of mempolicy object The tmpfs remount logic preserves filesystem mempolicy if the mpol=M option is not specified in the remount request. A new policy can be specified if mpol=M is given. Before this patch remounting an mpol bound tmpfs without specifying mpol= mount option in the remount request would set the filesystem's mempolicy object to a freed mempolicy object. To reproduce the problem boot a DEBUG_PAGEALLOC kernel and run: # mkdir /tmp/x # mount -t tmpfs -o size=100M,mpol=interleave nodev /tmp/x # grep /tmp/x /proc/mounts nodev /tmp/x tmpfs rw,relatime,size=102400k,mpol=interleave:0-3 0 0 # mount -o remount,size=200M nodev /tmp/x # grep /tmp/x /proc/mounts nodev /tmp/x tmpfs rw,relatime,size=204800k,mpol=??? 0 0 # note ? garbage in mpol=... output above # dd if=/dev/zero of=/tmp/x/f count=1 # panic here Panic: BUG: unable to handle kernel NULL pointer dereference at (null) IP: [< (null)>] (null) [...] Oops: 0010 [#1] SMP DEBUG_PAGEALLOC Call Trace: [<ffffffff81186ead>] ? mpol_set_nodemask+0x8d/0x100 [<ffffffff811895ef>] ? mpol_shared_policy_init+0x8f/0x160 [<ffffffff81189605>] mpol_shared_policy_init+0xa5/0x160 [<ffffffff811580e1>] ? shmem_get_inode+0x1e1/0x270 [<ffffffff811580e1>] ? shmem_get_inode+0x1e1/0x270 [<ffffffff810db15d>] ? trace_hardirqs_on+0xd/0x10 [<ffffffff81158109>] shmem_get_inode+0x209/0x270 [<ffffffff811581ae>] shmem_mknod+0x3e/0xf0 [<ffffffff811582b8>] shmem_create+0x18/0x20 [<ffffffff811af5d5>] vfs_create+0xb5/0x130 [<ffffffff811afff1>] do_last+0x9a1/0xea0 [<ffffffff811ac77a>] ? link_path_walk+0x7a/0x930 [<ffffffff811b05a3>] path_openat+0xb3/0x4d0 [<ffffffff811be831>] ? __alloc_fd+0x31/0x160 [<ffffffff811b0de2>] do_filp_open+0x42/0xa0 [<ffffffff811be8e0>] ? __alloc_fd+0xe0/0x160 [<ffffffff811a066e>] do_sys_open+0xfe/0x1e0 [<ffffffff811f0aeb>] compat_sys_open+0x1b/0x20 [<ffffffff815d6055>] cstar_dispatch+0x7/0x1f Non-debug kernels will not crash immediately because referencing the dangling mpol will not cause a fault. Instead the filesystem will reference a freed mempolicy object, which will cause unpredictable behavior. The problem boils down to a dropped mpol reference below if shmem_parse_options() does not allocate a new mpol: config = *sbinfo shmem_parse_options(data, &config, true) mpol_put(sbinfo->mpol) sbinfo->mpol = config.mpol /* BUG: saves unreferenced mpol */ This patch avoids the crash by not releasing the mempolicy if shmem_parse_options() doesn't create a new mpol. How far back does this issue go? I see it in both 2.6.36 and 3.3. I did not look back further. Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/shmem.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff -puN mm/shmem.c~tmpfs-fix-use-after-free-of-mempolicy-object mm/shmem.c --- a/mm/shmem.c~tmpfs-fix-use-after-free-of-mempolicy-object +++ a/mm/shmem.c @@ -2486,6 +2486,7 @@ static int shmem_remount_fs(struct super unsigned long inodes; int error = -EINVAL; + config.mpol = NULL; if (shmem_parse_options(data, &config, true)) return error; @@ -2510,8 +2511,13 @@ static int shmem_remount_fs(struct super sbinfo->max_inodes = config.max_inodes; sbinfo->free_inodes = config.max_inodes - inodes; - mpol_put(sbinfo->mpol); - sbinfo->mpol = config.mpol; /* transfers initial ref */ + /* + * Preserve previous mempolicy unless mpol remount option was specified. + */ + if (config.mpol) { + mpol_put(sbinfo->mpol); + sbinfo->mpol = config.mpol; /* transfers initial ref */ + } out: spin_unlock(&sbinfo->stat_lock); return error; _ Patches currently in -mm which might be from gthelen@xxxxxxxxxx are origin.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html