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slip: bound decode() reads against the compressed packet length 

slhc_uncompress() parses a VJ-compressed TCP header by advancing a
pointer through the packet via decode() and pull16(). Neither helper
bounds-checks against isize, and decode() masks its return with
& 0xffff so it can never return the -1 that callers test for -- those
error paths are dead code.

A short compressed frame whose change byte requests optional fields
lets decode() read past the end of the packet. The over-read bytes
are folded into the cached cstate and reflected into subsequent
reconstructed packets.

Make decode() and pull16() take the packet end pointer and return -1
when exhausted. Add a bounds check before the TCP-checksum read.
The existing == -1 tests now do what they were always meant to.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Reported-by: Simon Horman <horms@kernel.org>
Closes: https://lore.kernel.org/netdev/20260414134126.758795-2-horms@kernel.org/
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260416100147.531855-5-bestswngs@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
master
Weiming Shi 2026-04-16 18:01:51 +08:00 committed by Paolo Abeni
parent e76607442d
commit 4c1367a2d7
1 changed files with 25 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
drivers/net/slip/slhc.c
View File

@ -80,9 +80,9 @@
#include <linux/unaligned.h>
static unsigned char *encode(unsigned char *cp, unsigned short n);
static long decode(unsigned char **cpp);
static long decode(unsigned char **cpp, const unsigned char *end);
static unsigned char * put16(unsigned char *cp, unsigned short x);
static unsigned short pull16(unsigned char **cpp);
static long pull16(unsigned char **cpp, const unsigned char *end);
/* Allocate compression data structure
* slots must be in range 0 to 255 (zero meaning no compression)
@ -190,30 +190,34 @@ encode(unsigned char *cp, unsigned short n)
return cp;
}
/* Pull a 16-bit integer in host order from buffer in network byte order */
static unsigned short
pull16(unsigned char **cpp)
/* Pull a 16-bit integer in host order from buffer in network byte order.
* Returns -1 if the buffer is exhausted, otherwise the 16-bit value.
*/
static long
pull16(unsigned char **cpp, const unsigned char *end)
{
short rval;
long rval;
if (*cpp + 2 > end)
return -1;
rval = *(*cpp)++;
rval <<= 8;
rval |= *(*cpp)++;
return rval;
}
/* Decode a number */
/* Decode a number. Returns -1 if the buffer is exhausted. */
static long
decode(unsigned char **cpp)
decode(unsigned char **cpp, const unsigned char *end)
{
int x;
if (*cpp >= end)
return -1;
x = *(*cpp)++;
if(x == 0){
return pull16(cpp) & 0xffff; /* pull16 returns -1 on error */
} else {
return x & 0xff; /* -1 if PULLCHAR returned error */
}
if (x == 0)
return pull16(cpp, end);
return x & 0xff;
}
/*
@ -499,6 +503,7 @@ slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
struct cstate *cs;
int len, hdrlen;
unsigned char *cp = icp;
const unsigned char *end = icp + isize;
/* We've got a compressed packet; read the change byte */
comp->sls_i_compressed++;
@ -536,6 +541,8 @@ slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
thp = &cs->cs_tcp;
ip = &cs->cs_ip;
if (cp + 2 > end)
goto bad;
thp->check = *(__sum16 *)cp;
cp += 2;
@ -566,26 +573,26 @@ slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
default:
if(changes & NEW_U){
thp->urg = 1;
if((x = decode(&cp)) == -1) {
if((x = decode(&cp, end)) == -1) {
goto bad;
}
thp->urg_ptr = htons(x);
} else
thp->urg = 0;
if(changes & NEW_W){
if((x = decode(&cp)) == -1) {
if((x = decode(&cp, end)) == -1) {
goto bad;
}
thp->window = htons( ntohs(thp->window) + x);
}
if(changes & NEW_A){
if((x = decode(&cp)) == -1) {
if((x = decode(&cp, end)) == -1) {
goto bad;
}
thp->ack_seq = htonl( ntohl(thp->ack_seq) + x);
}
if(changes & NEW_S){
if((x = decode(&cp)) == -1) {
if((x = decode(&cp, end)) == -1) {
goto bad;
}
thp->seq = htonl( ntohl(thp->seq) + x);
@ -593,7 +600,7 @@ slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
break;
}
if(changes & NEW_I){
if((x = decode(&cp)) == -1) {
if((x = decode(&cp, end)) == -1) {
goto bad;
}
ip->id = htons (ntohs (ip->id) + x);