| Message ID | 201712032227.JCH90603.HQOOtVFMJOFLSF@I-love.SAKURA.ne.jp (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
On Sun, 3 Dec 2017, Tetsuo Handa wrote: > Tetsuo Handa wrote: > > which will allow strcmp() to trigger out of bound read when "size" is > > larger than strlen(initial_sid_to_string[i]). > > Oops. "smaller" than. > > > > > Thus, I guess the simplest fix is to use strncmp() instead of strcmp(). > > Can somebody test below patch? (My CentOS 7 environment does not support > enabling SELinux in linux.git . Userspace tool is too old to support?) You mean enabling KASAN? Yep, you need gcc 4.9.2 or better. Recent Fedora has it.
On Sun, Dec 3, 2017 at 2:27 PM, Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote: > Tetsuo Handa wrote: >> which will allow strcmp() to trigger out of bound read when "size" is >> larger than strlen(initial_sid_to_string[i]). > > Oops. "smaller" than. > >> >> Thus, I guess the simplest fix is to use strncmp() instead of strcmp(). > > Can somebody test below patch? (My CentOS 7 environment does not support > enabling SELinux in linux.git . Userspace tool is too old to support?) Hi Tetsuo, syzbot supports testing of patches. See footer of the first email in thread. > ---------- > >From 3efab617f7c22360361a2bd89a0ccaf3bcd47951 Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Date: Sun, 3 Dec 2017 22:12:17 +0900 > Subject: [PATCH] selinux: Fix out of bounds read at > security_context_to_sid_core() > > Syzbot caught an out of bounds read at security_context_to_sid_core() > because security_context_to_sid_core() assumed that the value written to > /proc/pid/attr interface is terminated with either '\0' or '\n'. > When the value is not terminated with either '\0' or '\n' and > scontext_len < strlen(initial_sid_to_string[i]) is true, strcmp() will > trigger out of bounds read. > > ---------- > BUG: KASAN: slab-out-of-bounds in strcmp+0x96/0xb0 lib/string.c:328 > Read of size 1 at addr ffff8801cd99d2c1 by task syzkaller242593/3087 > > CPU: 0 PID: 3087 Comm: syzkaller242593 Not tainted 4.15.0-rc1-next-20171201+ #57 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:17 [inline] > dump_stack+0x194/0x257 lib/dump_stack.c:53 > print_address_description+0x73/0x250 mm/kasan/report.c:252 > kasan_report_error mm/kasan/report.c:351 [inline] > kasan_report+0x25b/0x340 mm/kasan/report.c:409 > __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:427 > strcmp+0x96/0xb0 lib/string.c:328 > security_context_to_sid_core+0x437/0x620 security/selinux/ss/services.c:1420 > security_context_to_sid+0x32/0x40 security/selinux/ss/services.c:1479 > selinux_setprocattr+0x51c/0xb50 security/selinux/hooks.c:5986 > security_setprocattr+0x85/0xc0 security/security.c:1264 > proc_pid_attr_write+0x1e6/0x280 fs/proc/base.c:2574 > __vfs_write+0xef/0x970 fs/read_write.c:480 > __kernel_write+0xfe/0x350 fs/read_write.c:501 > write_pipe_buf+0x175/0x220 fs/splice.c:797 > splice_from_pipe_feed fs/splice.c:502 [inline] > __splice_from_pipe+0x328/0x730 fs/splice.c:626 > splice_from_pipe+0x1e9/0x330 fs/splice.c:661 > default_file_splice_write+0x40/0x90 fs/splice.c:809 > do_splice_from fs/splice.c:851 [inline] > direct_splice_actor+0x125/0x180 fs/splice.c:1018 > splice_direct_to_actor+0x2c1/0x820 fs/splice.c:973 > do_splice_direct+0x2a7/0x3d0 fs/splice.c:1061 > do_sendfile+0x5d5/0xe90 fs/read_write.c:1413 > SYSC_sendfile64 fs/read_write.c:1468 [inline] > SyS_sendfile64+0xbd/0x160 fs/read_write.c:1460 > entry_SYSCALL_64_fastpath+0x1f/0x96 > ---------- > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Reported-by: syzbot <syzkaller@googlegroups.com> > --- > security/selinux/ss/services.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c > index 33cfe5d..2b2ce3e 100644 > --- a/security/selinux/ss/services.c > +++ b/security/selinux/ss/services.c > @@ -1417,7 +1417,9 @@ static int security_context_to_sid_core(const char *scontext, u32 scontext_len, > int i; > > for (i = 1; i < SECINITSID_NUM; i++) { > - if (!strcmp(initial_sid_to_string[i], scontext)) { > + if (!strncmp(initial_sid_to_string[i], scontext, > + scontext_len) && > + !initial_sid_to_string[i][scontext_len]) { > *sid = i; > return 0; > } > -- > 1.8.3.1 > > -- > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/201712032227.JCH90603.HQOOtVFMJOFLSF%40I-love.SAKURA.ne.jp. > For more options, visit https://groups.google.com/d/optout.
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c index 33cfe5d..2b2ce3e 100644 --- a/security/selinux/ss/services.c +++ b/security/selinux/ss/services.c @@ -1417,7 +1417,9 @@ static int security_context_to_sid_core(const char *scontext, u32 scontext_len, int i; for (i = 1; i < SECINITSID_NUM; i++) { - if (!strcmp(initial_sid_to_string[i], scontext)) { + if (!strncmp(initial_sid_to_string[i], scontext, + scontext_len) && + !initial_sid_to_string[i][scontext_len]) { *sid = i; return 0; }