KEYS: Fix short sprintf buffer in /proc/keys show function (CVE-2016-7042)

debian/changelog

@@ -129,6 +129,9 @@ linux (4.7.7-1) UNRELEASED; urgency=medium
   * posix_acl: Clear SGID bit when setting file permissions (CVE-2016-7097)
   * scsi: arcmsr: Buffer overflow in arcmsr_iop_message_xfer() (CVE-2016-7425)
 
+  [ Salvatore Bonaccorso ]
+  * KEYS: Fix short sprintf buffer in /proc/keys show function (CVE-2016-7042)
+
  -- Ben Hutchings <ben@decadent.org.uk>  Tue, 11 Oct 2016 22:43:14 +0100
 
 linux (4.7.6-1) unstable; urgency=medium

debian/patches/bugfix/all/KEYS-Fix-short-sprintf-buffer-in-proc-keys-show-func.patch

@@ -0,0 +1,70 @@
+From: David Howells <dhowells@redhat.com>
+Date: Thu, 13 Oct 2016 22:38:46 +0200
+Subject: KEYS: Fix short sprintf buffer in /proc/keys show function
+Origin: https://bugzilla.redhat.com/attachment.cgi?id=1200212
+
+Fix a short sprintf buffer in proc_keys_show().  If the gcc stack protector
+is turned on, this can cause a panic due to stack corruption.
+
+The problem is that xbuf[] is not big enough to hold a 64-bit timeout
+rendered as weeks:
+
+	(gdb) p 0xffffffffffffffffULL/(60*60*24*7)
+	$2 = 30500568904943
+
+That's 14 chars plus NUL, not 11 chars plus NUL.
+
+Expand the buffer to 16 chars.
+
+I think the unpatched code apparently works if the stack-protector is not
+enabled because on a 32-bit machine the buffer won't be overflowed and on a
+64-bit machine there's a 64-bit aligned pointer at one side and an int that
+isn't checked again on the other side.
+
+The panic incurred looks something like:
+
+Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: ffffffff81352ebe
+CPU: 0 PID: 1692 Comm: reproducer Not tainted 4.7.2-201.fc24.x86_64 #1
+Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
+ 0000000000000086 00000000fbbd2679 ffff8800a044bc00 ffffffff813d941f
+ ffffffff81a28d58 ffff8800a044bc98 ffff8800a044bc88 ffffffff811b2cb6
+ ffff880000000010 ffff8800a044bc98 ffff8800a044bc30 00000000fbbd2679
+Call Trace:
+ [<ffffffff813d941f>] dump_stack+0x63/0x84
+ [<ffffffff811b2cb6>] panic+0xde/0x22a
+ [<ffffffff81352ebe>] ? proc_keys_show+0x3ce/0x3d0
+ [<ffffffff8109f7f9>] __stack_chk_fail+0x19/0x30
+ [<ffffffff81352ebe>] proc_keys_show+0x3ce/0x3d0
+ [<ffffffff81350410>] ? key_validate+0x50/0x50
+ [<ffffffff8134db30>] ? key_default_cmp+0x20/0x20
+ [<ffffffff8126b31c>] seq_read+0x2cc/0x390
+ [<ffffffff812b6b12>] proc_reg_read+0x42/0x70
+ [<ffffffff81244fc7>] __vfs_read+0x37/0x150
+ [<ffffffff81357020>] ? security_file_permission+0xa0/0xc0
+ [<ffffffff81246156>] vfs_read+0x96/0x130
+ [<ffffffff81247635>] SyS_read+0x55/0xc0
+ [<ffffffff817eb872>] entry_SYSCALL_64_fastpath+0x1a/0xa4
+
+Reported-by: Ondrej Kozina <okozina@redhat.com>
+Signed-off-by: David Howells <dhowells@redhat.com>
+Tested-by: Ondrej Kozina <okozina@redhat.com>
+---
+ security/keys/proc.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/security/keys/proc.c b/security/keys/proc.c
+index f0611a6..b9f531c 100644
+--- a/security/keys/proc.c
++++ b/security/keys/proc.c
+@@ -181,7 +181,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
+ 	struct timespec now;
+ 	unsigned long timo;
+ 	key_ref_t key_ref, skey_ref;
+-	char xbuf[12];
++	char xbuf[16];
+ 	int rc;
+ 
+ 	struct keyring_search_context ctx = {
+-- 
+2.9.3
+

debian/patches/series

@@ -117,6 +117,7 @@ debian/i386-686-pae-pci-set-pci-nobios-by-default.patch
 bugfix/all/net-add-recursion-limit-to-gro.patch
 bugfix/all/posix_acl-clear-sgid-bit-when-setting-file-permissio.patch
 bugfix/all/scsi-arcmsr-buffer-overflow-in-arcmsr_iop_message_xf.patch
+bugfix/all/KEYS-Fix-short-sprintf-buffer-in-proc-keys-show-func.patch
 
 # ABI maintenance
 debian/i8042-revert-abi-break-in-4.7.3.patch