path: root/kernel
diff options
authorDaniel Borkmann <>2014-04-14 21:02:59 +0200
committerDavid S. Miller <>2014-04-14 16:26:47 -0400
commit2eac7648321f4a08aa4078504d7727af0af7173b (patch)
tree297971645acc3bfbc6e9ac18ed95c78b83c6c5fa /kernel
parent14ed4a5bcbd56e87e7c56b4604f43e47162a2e54 (diff)
seccomp: fix populating a0-a5 syscall args in 32-bit x86 BPF
Linus reports that on 32-bit x86 Chromium throws the following seccomp resp. audit log messages: audit: type=1326 audit(1397359304.356:28108): auid=500 uid=500 gid=500 ses=2 subj=unconfined_u:unconfined_r:chrome_sandbox_t:s0-s0:c0.c1023 pid=3677 comm="chrome" exe="/opt/google/chrome/chrome" sig=0 syscall=172 compat=0 ip=0xb2dd9852 code=0x30000 audit: type=1326 audit(1397359304.356:28109): auid=500 uid=500 gid=500 ses=2 subj=unconfined_u:unconfined_r:chrome_sandbox_t:s0-s0:c0.c1023 pid=3677 comm="chrome" exe="/opt/google/chrome/chrome" sig=0 syscall=5 compat=0 ip=0xb2dd9852 code=0x50000 These audit messages are being triggered via audit_seccomp() through __secure_computing() in seccomp mode (BPF) filter with seccomp return codes 0x30000 (== SECCOMP_RET_TRAP) and 0x50000 (== SECCOMP_RET_ERRNO) during filter runtime. Moreover, Linus reports that x86_64 Chromium seems fine. The underlying issue that explains this is that the implementation of populate_seccomp_data() is wrong. Our seccomp data structure sd that is being shared with user ABI is: struct seccomp_data { int nr; __u32 arch; __u64 instruction_pointer; __u64 args[6]; }; Therefore, a simple cast to 'unsigned long *' for storing the value of the syscall argument via syscall_get_arguments() is just wrong as on 32-bit x86 (or any other 32bit arch), it would result in storing a0-a5 at wrong offsets in args[] member, and thus i) could leak stack memory to user space and ii) tampers with the logic of seccomp BPF programs that read out and check for syscall arguments: syscall_get_arguments(task, regs, 0, 1, (unsigned long *) &sd->args[0]); Tested on 32-bit x86 with Google Chrome, unfortunately only via remote test machine through slow ssh X forwarding, but it fixes the issue on my side. So fix it up by storing args in type correct variables, gcc is clever and optimizes the copy away in other cases, e.g. x86_64. Fixes: bd4cf0ed331a ("net: filter: rework/optimize internal BPF interpreter's instruction set") Reported-and-bisected-by: Linus Torvalds <> Signed-off-by: Daniel Borkmann <> Signed-off-by: Alexei Starovoitov <> Cc: Linus Torvalds <> Cc: Eric Paris <> Cc: James Morris <> Cc: Kees Cook <> Signed-off-by: David S. Miller <>
Diffstat (limited to 'kernel')
1 files changed, 8 insertions, 9 deletions
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index d8d046c0726a..590c37925084 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -69,18 +69,17 @@ static void populate_seccomp_data(struct seccomp_data *sd)
struct task_struct *task = current;
struct pt_regs *regs = task_pt_regs(task);
+ unsigned long args[6];
sd->nr = syscall_get_nr(task, regs);
sd->arch = syscall_get_arch();
- /* Unroll syscall_get_args to help gcc on arm. */
- syscall_get_arguments(task, regs, 0, 1, (unsigned long *) &sd->args[0]);
- syscall_get_arguments(task, regs, 1, 1, (unsigned long *) &sd->args[1]);
- syscall_get_arguments(task, regs, 2, 1, (unsigned long *) &sd->args[2]);
- syscall_get_arguments(task, regs, 3, 1, (unsigned long *) &sd->args[3]);
- syscall_get_arguments(task, regs, 4, 1, (unsigned long *) &sd->args[4]);
- syscall_get_arguments(task, regs, 5, 1, (unsigned long *) &sd->args[5]);
+ syscall_get_arguments(task, regs, 0, 6, args);
+ sd->args[0] = args[0];
+ sd->args[1] = args[1];
+ sd->args[2] = args[2];
+ sd->args[3] = args[3];
+ sd->args[4] = args[4];
+ sd->args[5] = args[5];
sd->instruction_pointer = KSTK_EIP(task);