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edumazetgregkh
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slip: make slhc_compress() more robust against malicious packets
[ Upstream commit 110a40d ] Before accessing various fields in IPV4 network header and TCP header, make sure the packet : - Has IP version 4 (ip->version == 4) - Has not a silly network length (ip->ihl >= 5) - Is big enough to hold network and transport headers - Has not a silly TCP header size (th->doff >= sizeof(struct tcphdr) / 4) syzbot reported : BUG: KMSAN: uninit-value in slhc_compress+0x5b9/0x2e60 drivers/net/slip/slhc.c:270 CPU: 0 PID: 11728 Comm: syz-executor231 Not tainted 5.6.0-rc2-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1c9/0x220 lib/dump_stack.c:118 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118 __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215 slhc_compress+0x5b9/0x2e60 drivers/net/slip/slhc.c:270 ppp_send_frame drivers/net/ppp/ppp_generic.c:1637 [inline] __ppp_xmit_process+0x1902/0x2970 drivers/net/ppp/ppp_generic.c:1495 ppp_xmit_process+0x147/0x2f0 drivers/net/ppp/ppp_generic.c:1516 ppp_write+0x6bb/0x790 drivers/net/ppp/ppp_generic.c:512 do_loop_readv_writev fs/read_write.c:717 [inline] do_iter_write+0x812/0xdc0 fs/read_write.c:1000 compat_writev+0x2df/0x5a0 fs/read_write.c:1351 do_compat_pwritev64 fs/read_write.c:1400 [inline] __do_compat_sys_pwritev fs/read_write.c:1420 [inline] __se_compat_sys_pwritev fs/read_write.c:1414 [inline] __ia32_compat_sys_pwritev+0x349/0x3f0 fs/read_write.c:1414 do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline] do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410 entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139 RIP: 0023:0xf7f7cd99 Code: 90 e8 0b 00 00 00 f3 90 0f ae e8 eb f9 8d 74 26 00 89 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 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:00000000ffdb84ac EFLAGS: 00000217 ORIG_RAX: 000000000000014e RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000200001c0 RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000003 RBP: 0000000040047459 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 Uninit was created at: kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline] kmsan_internal_poison_shadow+0x66/0xd0 mm/kmsan/kmsan.c:127 kmsan_slab_alloc+0x8a/0xe0 mm/kmsan/kmsan_hooks.c:82 slab_alloc_node mm/slub.c:2793 [inline] __kmalloc_node_track_caller+0xb40/0x1200 mm/slub.c:4401 __kmalloc_reserve net/core/skbuff.c:142 [inline] __alloc_skb+0x2fd/0xac0 net/core/skbuff.c:210 alloc_skb include/linux/skbuff.h:1051 [inline] ppp_write+0x115/0x790 drivers/net/ppp/ppp_generic.c:500 do_loop_readv_writev fs/read_write.c:717 [inline] do_iter_write+0x812/0xdc0 fs/read_write.c:1000 compat_writev+0x2df/0x5a0 fs/read_write.c:1351 do_compat_pwritev64 fs/read_write.c:1400 [inline] __do_compat_sys_pwritev fs/read_write.c:1420 [inline] __se_compat_sys_pwritev fs/read_write.c:1414 [inline] __ia32_compat_sys_pwritev+0x349/0x3f0 fs/read_write.c:1414 do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline] do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410 entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139 Fixes: b5451d7 ("slip: Move the SLIP drivers") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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drivers/net/slip/slhc.c

Lines changed: 10 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -232,7 +232,7 @@ slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
232232
struct cstate *cs = lcs->next;
233233
unsigned long deltaS, deltaA;
234234
short changes = 0;
235-
int hlen;
235+
int nlen, hlen;
236236
unsigned char new_seq[16];
237237
unsigned char *cp = new_seq;
238238
struct iphdr *ip;
@@ -248,6 +248,8 @@ slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
248248
return isize;
249249

250250
ip = (struct iphdr *) icp;
251+
if (ip->version != 4 || ip->ihl < 5)
252+
return isize;
251253

252254
/* Bail if this packet isn't TCP, or is an IP fragment */
253255
if (ip->protocol != IPPROTO_TCP || (ntohs(ip->frag_off) & 0x3fff)) {
@@ -258,10 +260,14 @@ slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
258260
comp->sls_o_tcp++;
259261
return isize;
260262
}
261-
/* Extract TCP header */
263+
nlen = ip->ihl * 4;
264+
if (isize < nlen + sizeof(*th))
265+
return isize;
262266

263-
th = (struct tcphdr *)(((unsigned char *)ip) + ip->ihl*4);
264-
hlen = ip->ihl*4 + th->doff*4;
267+
th = (struct tcphdr *)(icp + nlen);
268+
if (th->doff < sizeof(struct tcphdr) / 4)
269+
return isize;
270+
hlen = nlen + th->doff * 4;
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266272
/* Bail if the TCP packet isn't `compressible' (i.e., ACK isn't set or
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* some other control bit is set). Also uncompressible if

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