6.17-stable review patch. If anyone has any objections, please let me know.
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From: Anderson Nascimento anderson@allelesecurity.com
[ Upstream commit 62e59ffe8787b5550ccff70c30b6f6be6a3ac3dd ]
The function do_fanotify_mark() does not validate if mnt_ns_from_dentry() returns NULL before dereferencing mntns->user_ns. This causes a NULL pointer dereference in do_fanotify_mark() if the path is not a mount namespace object.
Fix this by checking mnt_ns_from_dentry()'s return value before dereferencing it.
Before the patch
$ gcc fanotify_nullptr.c -o fanotify_nullptr $ mkdir A $ ./fanotify_nullptr Fanotify fd: 3 fanotify_mark: Operation not permitted $ unshare -Urm Fanotify fd: 3 Killed
int main(void){ int ffd; ffd = fanotify_init(FAN_CLASS_NOTIF | FAN_REPORT_MNT, 0); if(ffd < 0){ perror("fanotify_init"); exit(EXIT_FAILURE); }
printf("Fanotify fd: %d\n",ffd);
if(fanotify_mark(ffd, FAN_MARK_ADD | FAN_MARK_MNTNS, FAN_MNT_ATTACH, AT_FDCWD, "A") < 0){ perror("fanotify_mark"); exit(EXIT_FAILURE); }
return 0; }
After the patch
$ gcc fanotify_nullptr.c -o fanotify_nullptr $ mkdir A $ ./fanotify_nullptr Fanotify fd: 3 fanotify_mark: Operation not permitted $ unshare -Urm Fanotify fd: 3 fanotify_mark: Invalid argument
[ 25.694973] BUG: kernel NULL pointer dereference, address: 0000000000000038 [ 25.695006] #PF: supervisor read access in kernel mode [ 25.695012] #PF: error_code(0x0000) - not-present page [ 25.695017] PGD 109a30067 P4D 109a30067 PUD 142b46067 PMD 0 [ 25.695025] Oops: Oops: 0000 [#1] SMP NOPTI [ 25.695032] CPU: 4 UID: 1000 PID: 1478 Comm: fanotify_nullpt Not tainted 6.17.0-rc4 #1 PREEMPT(lazy) [ 25.695040] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 [ 25.695049] RIP: 0010:do_fanotify_mark+0x817/0x950 [ 25.695066] Code: 04 00 00 e9 45 fd ff ff 48 8b 7c 24 48 4c 89 54 24 18 4c 89 5c 24 10 4c 89 0c 24 e8 b3 11 fc ff 4c 8b 54 24 18 4c 8b 5c 24 10 <48> 8b 78 38 4c 8b 0c 24 49 89 c4 e9 13 fd ff ff 8b 4c 24 28 85 c9 [ 25.695081] RSP: 0018:ffffd31c469e3c08 EFLAGS: 00010203 [ 25.695104] RAX: 0000000000000000 RBX: 0000000001000000 RCX: ffff8eb48aebd220 [ 25.695110] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8eb4835e8180 [ 25.695115] RBP: 0000000000000111 R08: 0000000000000000 R09: 0000000000000000 [ 25.695142] R10: ffff8eb48a7d56c0 R11: ffff8eb482bede00 R12: 00000000004012a7 [ 25.695148] R13: 0000000000000110 R14: 0000000000000001 R15: ffff8eb48a7d56c0 [ 25.695154] FS: 00007f8733bda740(0000) GS:ffff8eb61ce5f000(0000) knlGS:0000000000000000 [ 25.695162] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 25.695170] CR2: 0000000000000038 CR3: 0000000136994006 CR4: 00000000003706f0 [ 25.695201] Call Trace: [ 25.695209] <TASK> [ 25.695215] __x64_sys_fanotify_mark+0x1f/0x30 [ 25.695222] do_syscall_64+0x82/0x2c0 ...
Fixes: 58f5fbeb367f ("fanotify: support watching filesystems and mounts inside userns") Link: https://patch.msgid.link/CAPhRvkw4ONypNsJrCnxbKnJbYmLHTDEKFC4C_num_5sVBVa8jg... Signed-off-by: Anderson Nascimento anderson@allelesecurity.com Reviewed-by: Christian Brauner brauner@kernel.org Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Sasha Levin sashal@kernel.org --- fs/notify/fanotify/fanotify_user.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index b192ee068a7ac..561339b4cf752 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -1999,7 +1999,10 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask, user_ns = path.mnt->mnt_sb->s_user_ns; obj = path.mnt->mnt_sb; } else if (obj_type == FSNOTIFY_OBJ_TYPE_MNTNS) { + ret = -EINVAL; mntns = mnt_ns_from_dentry(path.dentry); + if (!mntns) + goto path_put_and_out; user_ns = mntns->user_ns; obj = mntns; }