CVE-2014-7826: NULL Pointer Dereference (CWE-476)
value: kernel/trace/trace_syscalls.c in the Linux kernel through 3.17.2 does not properly handle private syscall numbers during use of the ftrace subsystem, which allows local users to gain privileges or cause a denial of service (invalid pointer dereference) via a crafted application.
CWE description: The product dereferences a pointer that it expects to be valid but is NULL.
CVSS v3 base score: 7.8
Published: 2014-11-10T11:55Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: kernel/trace/trace_syscalls.c
Commit date: 2014-10-30 20:58:38 -0400
Commit message: tracing/syscalls: Ignore numbers outside NR_syscalls' range

ARM has some private syscalls (for example, set_tls(2)) which lie
outside the range of NR_syscalls.  If any of these are called while
syscall tracing is being performed, out-of-bounds array access will
occur in the ftrace and perf sys_{enter,exit} handlers.

 # trace-cmd record -e raw_syscalls:* true && trace-cmd report
 ...
 true-653   [000]   384.675777: sys_enter:            NR 192 (0, 1000, 3, 4000022, ffffffff, 0)
 true-653   [000]   384.675812: sys_exit:             NR 192 = 1995915264
 true-653   [000]   384.675971: sys_enter:            NR 983045 (76f74480, 76f74000, 76f74b28, 76f74480, 76f76f74, 1)
 true-653   [000]   384.675988: sys_exit:             NR 983045 = 0
 ...

 # trace-cmd record -e syscalls:* true
 [   17.289329] Unable to handle kernel paging request at virtual address aaaaaace
 [   17.289590] pgd = 9e71c000
 [   17.289696] [aaaaaace] *pgd=00000000
 [   17.289985] Internal error: Oops: 5 [#1] PREEMPT SMP ARM
 [   17.290169] Modules linked in:
 [   17.290391] CPU: 0 PID: 704 Comm: true Not tainted 3.18.0-rc2+ #21
 [   17.290585] task: 9f4dab00 ti: 9e710000 task.ti: 9e710000
 [   17.290747] PC is at ftrace_syscall_enter+0x48/0x1f8
 [   17.290866] LR is at syscall_trace_enter+0x124/0x184

Fix this by ignoring out-of-NR_syscalls-bounds syscall numbers.

Commit cd0980fc8add "tracing: Check invalid syscall nr while tracing syscalls"
added the check for less than zero, but it should have also checked
for greater than NR_syscalls.

Link: http://lkml.kernel.org/p/1414620418-29472-1-git-send-email-rabin@rab.in

Fixes: cd0980fc8add "tracing: Check invalid syscall nr while tracing syscalls"
Cc: stable@vger.kernel.org # 2.6.33+
Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Diff: diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 4dc8b79c5f75d2..29228c4d569692 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -311,11 +311,11 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
 	int pc;
 	int syscall_nr;
 	int size;
 
 	syscall_nr = trace_get_syscall_nr(current, regs);
-	if (syscall_nr < 0)
+	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
 		return;
 
 	/* Here we're inside tp handler's rcu_read_lock_sched (__DO_TRACE) */
 	ftrace_file = rcu_dereference_sched(tr->enter_syscall_files[syscall_nr]);
 	if (!ftrace_file)
@@ -358,11 +358,11 @@ static void ftrace_syscall_exit(void *data, struct pt_regs *regs, long ret)
 	unsigned long irq_flags;
 	int pc;
 	int syscall_nr;
 
 	syscall_nr = trace_get_syscall_nr(current, regs);
-	if (syscall_nr < 0)
+	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
 		return;
 
 	/* Here we're inside tp handler's rcu_read_lock_sched (__DO_TRACE()) */
 	ftrace_file = rcu_dereference_sched(tr->exit_syscall_files[syscall_nr]);
 	if (!ftrace_file)
@@ -565,11 +565,11 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	int syscall_nr;
 	int rctx;
 	int size;
 
 	syscall_nr = trace_get_syscall_nr(current, regs);
-	if (syscall_nr < 0)
+	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
 		return;
 	if (!test_bit(syscall_nr, enabled_perf_enter_syscalls))
 		return;
 
 	sys_data = syscall_nr_to_meta(syscall_nr);
@@ -639,11 +639,11 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 	int syscall_nr;
 	int rctx;
 	int size;
 
 	syscall_nr = trace_get_syscall_nr(current, regs);
-	if (syscall_nr < 0)
+	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
 		return;
 	if (!test_bit(syscall_nr, enabled_perf_exit_syscalls))
 		return;
 
 	sys_data = syscall_nr_to_meta(syscall_nr);

Vulnerable code: 	if (syscall_nr < 0)
	if (syscall_nr < 0)
	if (syscall_nr < 0)
	if (syscall_nr < 0)
Fixed code: 	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)