From: Mathias Krause Date: Tue, 12 Nov 2013 23:11:47 +0000 (-0800) Subject: ipc, msg: fix message length check for negative values X-Git-Tag: v3.2.54~124 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=f2414ee66a2901b376845bfec33f33b2a79fd004 ipc, msg: fix message length check for negative values commit 4e9b45a19241354daec281d7a785739829b52359 upstream. On 64 bit systems the test for negative message sizes is bogus as the size, which may be positive when evaluated as a long, will get truncated to an int when passed to load_msg(). So a long might very well contain a positive value but when truncated to an int it would become negative. That in combination with a small negative value of msg_ctlmax (which will be promoted to an unsigned type for the comparison against msgsz, making it a big positive value and therefore make it pass the check) will lead to two problems: 1/ The kmalloc() call in alloc_msg() will allocate a too small buffer as the addition of alen is effectively a subtraction. 2/ The copy_from_user() call in load_msg() will first overflow the buffer with userland data and then, when the userland access generates an access violation, the fixup handler copy_user_handle_tail() will try to fill the remainder with zeros -- roughly 4GB. That almost instantly results in a system crash or reset. ,-[ Reproducer (needs to be run as root) ]-- | #include | #include | #include | #include | | int main(void) { | long msg = 1; | int fd; | | fd = open("/proc/sys/kernel/msgmax", O_WRONLY); | write(fd, "-1", 2); | close(fd); | | msgsnd(0, &msg, 0xfffffff0, IPC_NOWAIT); | | return 0; | } '--- Fix the issue by preventing msgsz from getting truncated by consistently using size_t for the message length. This way the size checks in do_msgsnd() could still be passed with a negative value for msg_ctlmax but we would fail on the buffer allocation in that case and error out. Also change the type of m_ts from int to size_t to avoid similar nastiness in other code paths -- it is used in similar constructs, i.e. signed vs. unsigned checks. It should never become negative under normal circumstances, though. Setting msg_ctlmax to a negative value is an odd configuration and should be prevented. As that might break existing userland, it will be handled in a separate commit so it could easily be reverted and reworked without reintroducing the above described bug. Hardening mechanisms for user copy operations would have catched that bug early -- e.g. checking slab object sizes on user copy operations as the usercopy feature of the PaX patch does. Or, for that matter, detect the long vs. int sign change due to truncation, as the size overflow plugin of the very same patch does. [akpm@linux-foundation.org: fix i386 min() warnings] Signed-off-by: Mathias Krause Cc: Pax Team Cc: Davidlohr Bueso Cc: Brad Spengler Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: - Adjust context - Drop changes to alloc_msg() and copy_msg(), which don't exist] Signed-off-by: Ben Hutchings --- diff --git a/include/linux/msg.h b/include/linux/msg.h index 56abf1558fdd..70fc369ad24f 100644 --- a/include/linux/msg.h +++ b/include/linux/msg.h @@ -76,9 +76,9 @@ struct msginfo { /* one msg_msg structure for each message */ struct msg_msg { - struct list_head m_list; - long m_type; - int m_ts; /* message text size */ + struct list_head m_list; + long m_type; + size_t m_ts; /* message text size */ struct msg_msgseg* next; void *security; /* the actual message follows immediately */ diff --git a/ipc/msgutil.c b/ipc/msgutil.c index 5652101cdac0..fc6fded4ff03 100644 --- a/ipc/msgutil.c +++ b/ipc/msgutil.c @@ -37,15 +37,15 @@ struct msg_msgseg { /* the next part of the message follows immediately */ }; -#define DATALEN_MSG (PAGE_SIZE-sizeof(struct msg_msg)) -#define DATALEN_SEG (PAGE_SIZE-sizeof(struct msg_msgseg)) +#define DATALEN_MSG ((size_t)PAGE_SIZE-sizeof(struct msg_msg)) +#define DATALEN_SEG ((size_t)PAGE_SIZE-sizeof(struct msg_msgseg)) -struct msg_msg *load_msg(const void __user *src, int len) +struct msg_msg *load_msg(const void __user *src, size_t len) { struct msg_msg *msg; struct msg_msgseg **pseg; int err; - int alen; + size_t alen; alen = len; if (alen > DATALEN_MSG) @@ -99,9 +99,9 @@ out_err: return ERR_PTR(err); } -int store_msg(void __user *dest, struct msg_msg *msg, int len) +int store_msg(void __user *dest, struct msg_msg *msg, size_t len) { - int alen; + size_t alen; struct msg_msgseg *seg; alen = len; diff --git a/ipc/util.h b/ipc/util.h index 6f5c20bedaab..0bfc934c2f45 100644 --- a/ipc/util.h +++ b/ipc/util.h @@ -138,8 +138,8 @@ int ipc_parse_version (int *cmd); #endif extern void free_msg(struct msg_msg *msg); -extern struct msg_msg *load_msg(const void __user *src, int len); -extern int store_msg(void __user *dest, struct msg_msg *msg, int len); +extern struct msg_msg *load_msg(const void __user *src, size_t len); +extern int store_msg(void __user *dest, struct msg_msg *msg, size_t len); extern void recompute_msgmni(struct ipc_namespace *);