From: Kees Cook keescook@chromium.org
[ Upstream commit a318f12ed8843cfac53198390c74a565c632f417 ]
Andreas Christoforou reported:
UBSAN: Undefined behaviour in ipc/mqueue.c:414:49 signed integer overflow: 9 * 2305843009213693951 cannot be represented in type 'long int' ... Call Trace: mqueue_evict_inode+0x8e7/0xa10 ipc/mqueue.c:414 evict+0x472/0x8c0 fs/inode.c:558 iput_final fs/inode.c:1547 [inline] iput+0x51d/0x8c0 fs/inode.c:1573 mqueue_get_inode+0x8eb/0x1070 ipc/mqueue.c:320 mqueue_create_attr+0x198/0x440 ipc/mqueue.c:459 vfs_mkobj+0x39e/0x580 fs/namei.c:2892 prepare_open ipc/mqueue.c:731 [inline] do_mq_open+0x6da/0x8e0 ipc/mqueue.c:771
Which could be triggered by:
struct mq_attr attr = { .mq_flags = 0, .mq_maxmsg = 9, .mq_msgsize = 0x1fffffffffffffff, .mq_curmsgs = 0, };
if (mq_open("/testing", 0x40, 3, &attr) == (mqd_t) -1) perror("mq_open");
mqueue_get_inode() was correctly rejecting the giant mq_msgsize, and preparing to return -EINVAL. During the cleanup, it calls mqueue_evict_inode() which performed resource usage tracking math for updating "user", before checking if there was a valid "user" at all (which would indicate that the calculations would be sane). Instead, delay this check to after seeing a valid "user".
The overflow was real, but the results went unused, so while the flaw is harmless, it's noisy for kernel fuzzers, so just fix it by moving the calculation under the non-NULL "user" where it actually gets used.
Link: http://lkml.kernel.org/r/201906072207.ECB65450@keescook Signed-off-by: Kees Cook keescook@chromium.org Reported-by: Andreas Christoforou andreaschristofo@gmail.com Acked-by: "Eric W. Biederman" ebiederm@xmission.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Arnd Bergmann arnd@arndb.de Cc: Davidlohr Bueso dave@stgolabs.net Cc: Manfred Spraul manfred@colorfullife.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- ipc/mqueue.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-)
diff --git a/ipc/mqueue.c b/ipc/mqueue.c index 216cad1ff0d0..65c351564ad0 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -438,7 +438,6 @@ static void mqueue_evict_inode(struct inode *inode) { struct mqueue_inode_info *info; struct user_struct *user; - unsigned long mq_bytes, mq_treesize; struct ipc_namespace *ipc_ns; struct msg_msg *msg, *nmsg; LIST_HEAD(tmp_msg); @@ -461,16 +460,18 @@ static void mqueue_evict_inode(struct inode *inode) free_msg(msg); }
- /* Total amount of bytes accounted for the mqueue */ - mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) + - min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) * - sizeof(struct posix_msg_tree_node); - - mq_bytes = mq_treesize + (info->attr.mq_maxmsg * - info->attr.mq_msgsize); - user = info->user; if (user) { + unsigned long mq_bytes, mq_treesize; + + /* Total amount of bytes accounted for the mqueue */ + mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) + + min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) * + sizeof(struct posix_msg_tree_node); + + mq_bytes = mq_treesize + (info->attr.mq_maxmsg * + info->attr.mq_msgsize); + spin_lock(&mq_lock); user->mq_bytes -= mq_bytes; /*