KASAN: vmalloc-out-of-bounds Read in compat_copy_entries

KASAN: vmalloc-out-of-bounds Read in compat_copy_entries

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    e31736d9 Merge tag 'nios2-v5.5-rc2' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14a4f5dee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=f68108fed972453a0ad4
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11c105dee00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12f1e32ee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f68108fed972453a0ad4@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in size_entry_mwt  
net/bridge/netfilter/ebtables.c:2063 [inline]
BUG: KASAN: vmalloc-out-of-bounds in compat_copy_entries+0x128b/0x1380  
net/bridge/netfilter/ebtables.c:2155
Read of size 4 at addr ffffc900004461f4 by task syz-executor267/7937

CPU: 1 PID: 7937 Comm: syz-executor267 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS  
rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x197/0x210 lib/dump_stack.c:118
  print_address_description.constprop.0.cold+0x5/0x30b mm/kasan/report.c:374
  __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
  kasan_report+0x12/0x20 mm/kasan/common.c:639
  __asan_report_load4_noabort+0x14/0x20 mm/kasan/generic_report.c:134
  size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline]
  compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155
  compat_do_replace+0x344/0x720 net/bridge/netfilter/ebtables.c:2249
  compat_do_ebt_set_ctl+0x22f/0x27e net/bridge/netfilter/ebtables.c:2333
  compat_nf_sockopt net/netfilter/nf_sockopt.c:144 [inline]
  compat_nf_setsockopt+0x98/0x140 net/netfilter/nf_sockopt.c:156
  compat_ip_setsockopt net/ipv4/ip_sockglue.c:1286 [inline]
  compat_ip_setsockopt+0x106/0x140 net/ipv4/ip_sockglue.c:1267
  compat_udp_setsockopt+0x68/0xb0 net/ipv4/udp.c:2649
  compat_sock_common_setsockopt+0xb2/0x140 net/core/sock.c:3160
  __compat_sys_setsockopt+0x185/0x380 net/compat.c:384
  __do_compat_sys_setsockopt net/compat.c:397 [inline]
  __se_compat_sys_setsockopt net/compat.c:394 [inline]
  __ia32_compat_sys_setsockopt+0xbd/0x150 net/compat.c:394
  do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
  do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408
  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7fc3a39
Code: 00 00 00 89 d3 5b 5e 5f 5d c3 b8 80 96 98 00 eb c4 8b 04 24 c3 8b 1c  
24 c3 8b 34 24 c3 8b 3c 24 c3 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90  
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000ffab2b4c EFLAGS: 00000296 ORIG_RAX: 000000000000016e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000000000
RDX: 0000000000000080 RSI: 0000000020000240 RDI: 0000000000000212
RBP: 0000000000000012 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000


Memory state around the buggy address:
  ffffc90000446080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ffffc90000446100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffffc90000446180: 00 00 00 00 00 00 00 00 02 f9 f9 f9 f9 f9 f9 f9
                                                              ^
  ffffc90000446200: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  ffffc90000446280: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
==================================================================


---
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[PATCH nf] netfilter: ebtables: compat: reject all padding in matches/watchers

[Florian Westphal]

syzbot reported following splat:

BUG: KASAN: vmalloc-out-of-bounds in size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline]
BUG: KASAN: vmalloc-out-of-bounds in compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155
Read of size 4 at addr ffffc900004461f4 by task syz-executor267/7937

CPU: 1 PID: 7937 Comm: syz-executor267 Not tainted 5.5.0-rc1-syzkaller #0
 size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline]
 compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155
 compat_do_replace+0x344/0x720 net/bridge/netfilter/ebtables.c:2249
 compat_do_ebt_set_ctl+0x22f/0x27e net/bridge/netfilter/ebtables.c:2333
 [..]

Because padding isn't considered during computation of ->buf_user_offset,
"total" is decremented by fewer bytes than it should.

Therefore, the first part of

if (*total < sizeof(*entry) || entry->next_offset < sizeof(*entry))

will pass, -- it should not have.  This causes oob access:
entry->next_offset is past the vmalloced size.

Reject padding and check that computed user offset (sum of ebt_entry
structure plus all individual matches/watchers/targets) is same
value that userspace gave us as the offset of the next entry.

Reported-by: syzbot+f68108fed972453a0ad4@syzkaller.appspotmail.com
Fixes: 81e675c227ec ("netfilter: ebtables: add CONFIG_COMPAT support")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/bridge/netfilter/ebtables.c | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 4096d8a74a2b..e1256e03a9a8 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1867,7 +1867,7 @@ static int ebt_buf_count(struct ebt_entries_buf_state *state, unsigned int sz)
 }
 
 static int ebt_buf_add(struct ebt_entries_buf_state *state,
-		       void *data, unsigned int sz)
+		       const void *data, unsigned int sz)
 {
 	if (state->buf_kern_start == NULL)
 		goto count_only;
@@ -1901,7 +1901,7 @@ enum compat_mwt {
 	EBT_COMPAT_TARGET,
 };
 
-static int compat_mtw_from_user(struct compat_ebt_entry_mwt *mwt,
+static int compat_mtw_from_user(const struct compat_ebt_entry_mwt *mwt,
 				enum compat_mwt compat_mwt,
 				struct ebt_entries_buf_state *state,
 				const unsigned char *base)
@@ -1979,22 +1979,23 @@ static int compat_mtw_from_user(struct compat_ebt_entry_mwt *mwt,
 /* return size of all matches, watchers or target, including necessary
  * alignment and padding.
  */
-static int ebt_size_mwt(struct compat_ebt_entry_mwt *match32,
+static int ebt_size_mwt(const struct compat_ebt_entry_mwt *match32,
 			unsigned int size_left, enum compat_mwt type,
 			struct ebt_entries_buf_state *state, const void *base)
 {
+	const char *buf = (const char *)match32;
 	int growth = 0;
-	char *buf;
 
 	if (size_left == 0)
 		return 0;
 
-	buf = (char *) match32;
-
-	while (size_left >= sizeof(*match32)) {
+	do {
 		struct ebt_entry_match *match_kern;
 		int ret;
 
+		if (size_left < sizeof(*match32))
+			return -EINVAL;
+
 		match_kern = (struct ebt_entry_match *) state->buf_kern_start;
 		if (match_kern) {
 			char *tmp;
@@ -2031,22 +2032,18 @@ static int ebt_size_mwt(struct compat_ebt_entry_mwt *match32,
 		if (match_kern)
 			match_kern->match_size = ret;
 
-		/* rule should have no remaining data after target */
-		if (type == EBT_COMPAT_TARGET && size_left)
-			return -EINVAL;
-
 		match32 = (struct compat_ebt_entry_mwt *) buf;
-	}
+	} while (size_left);
 
 	return growth;
 }
 
 /* called for all ebt_entry structures. */
-static int size_entry_mwt(struct ebt_entry *entry, const unsigned char *base,
+static int size_entry_mwt(const struct ebt_entry *entry, const unsigned char *base,
 			  unsigned int *total,
 			  struct ebt_entries_buf_state *state)
 {
-	unsigned int i, j, startoff, new_offset = 0;
+	unsigned int i, j, startoff, next_expected_off, new_offset = 0;
 	/* stores match/watchers/targets & offset of next struct ebt_entry: */
 	unsigned int offsets[4];
 	unsigned int *offsets_update = NULL;
@@ -2132,11 +2129,13 @@ static int size_entry_mwt(struct ebt_entry *entry, const unsigned char *base,
 			return ret;
 	}
 
-	startoff = state->buf_user_offset - startoff;
+	next_expected_off = state->buf_user_offset - startoff;
+	if (next_expected_off != entry->next_offset)
+		return -EINVAL;
 
-	if (WARN_ON(*total < startoff))
+	if (*total < entry->next_offset)
 		return -EINVAL;
-	*total -= startoff;
+	*total -= entry->next_offset;
 	return 0;
 }
 
-- 
2.23.0

Re: KASAN: vmalloc-out-of-bounds Read in compat_copy_entries

[syzbot]

syzbot has bisected this bug to:

commit 0609ae011deb41c9629b7f5fd626dfa1ac9d16b0
Author: Daniel Axtens <dja@axtens.net>
Date:   Sun Dec 1 01:55:00 2019 +0000

     x86/kasan: support KASAN_VMALLOC

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=166d43dee00000
start commit:   e31736d9 Merge tag 'nios2-v5.5-rc2' of git://git.kernel.or..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=156d43dee00000
console output: https://syzkaller.appspot.com/x/log.txt?x=116d43dee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=f68108fed972453a0ad4
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16bc5946e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17302361e00000

Reported-by: syzbot+f68108fed972453a0ad4@syzkaller.appspotmail.com
Fixes: 0609ae011deb ("x86/kasan: support KASAN_VMALLOC")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [PATCH nf] netfilter: ebtables: compat: reject all padding in matches/watchers

[Pablo Neira Ayuso]

On Sun, Dec 15, 2019 at 03:49:25AM +0100, Florian Westphal wrote:
> syzbot reported following splat:
> 
> BUG: KASAN: vmalloc-out-of-bounds in size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline]
> BUG: KASAN: vmalloc-out-of-bounds in compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155
> Read of size 4 at addr ffffc900004461f4 by task syz-executor267/7937
> 
> CPU: 1 PID: 7937 Comm: syz-executor267 Not tainted 5.5.0-rc1-syzkaller #0
>  size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline]
>  compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155
>  compat_do_replace+0x344/0x720 net/bridge/netfilter/ebtables.c:2249
>  compat_do_ebt_set_ctl+0x22f/0x27e net/bridge/netfilter/ebtables.c:2333
>  [..]
> 
> Because padding isn't considered during computation of ->buf_user_offset,
> "total" is decremented by fewer bytes than it should.
> 
> Therefore, the first part of
> 
> if (*total < sizeof(*entry) || entry->next_offset < sizeof(*entry))
> 
> will pass, -- it should not have.  This causes oob access:
> entry->next_offset is past the vmalloced size.
> 
> Reject padding and check that computed user offset (sum of ebt_entry
> structure plus all individual matches/watchers/targets) is same
> value that userspace gave us as the offset of the next entry.

Applied, thanks.