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net/sched: fix pedit partial COW leading to page cache corruption

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tcf_pedit_act() computes the COW range for skb_ensure_writable()
once before the key loop using tcfp_off_max_hint, but the hint does
not account for the runtime header offset added by typed keys. This
can leave part of the write region un-COW'd.

Fix by moving skb_ensure_writable() inside the per-key loop where
the actual write offset is known, and add overflow checking on the
offset arithmetic. For negative offsets (e.g. Ethernet header edits
at ingress), use skb_cow() to COW the headroom instead. Guard
offset_valid() against INT_MIN, where negation is undefined.

Fixes: 8b796475fd ("net/sched: act_pedit: really ensure the skb is writable")
Reported-by: Yiming Qian <yimingqian591@gmail.com>
Reported-by: Keenan Dong <keenanat2000@gmail.com>
Reported-by: Han Guidong <2045gemini@gmail.com>
Reported-by: Zhang Cen <rollkingzzc@gmail.com>
Reviewed-by: Han Guidong <2045gemini@gmail.com>
Tested-by: Han Guidong <2045gemini@gmail.com>
Reviewed-by: Davide Caratti <dcaratti@redhat.com>
Tested-by: Davide Caratti <dcaratti@redhat.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Tested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Rajat Gupta <rajat.gupta@oss.qualcomm.com>
Link: https://patch.msgid.link/20260531123221.48732-1-jhs@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Rajat Gupta
2026-05-31 08:32:21 -04:00
committed by Jakub Kicinski
parent c05fa14db4
commit 899ee91156
2 changed files with 41 additions and 37 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/net/tc_act/tc_pedit.h
-1
View File
@@ -15,7 +15,6 @@ struct tcf_pedit_parms {
struct tc_pedit_key *tcfp_keys;
struct tcf_pedit_key_ex *tcfp_keys_ex;
int action;
u32 tcfp_off_max_hint;
unsigned char tcfp_nkeys;
unsigned char tcfp_flags;
struct rcu_head rcu;
net/sched/act_pedit.c
+41 -36
View File
@@ -16,6 +16,8 @@
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/slab.h>
#include <linux/overflow.h>
#include <linux/unaligned.h>
#include <net/ipv6.h>
#include <net/netlink.h>
#include <net/pkt_sched.h>
@@ -242,7 +244,6 @@ static int tcf_pedit_init(struct net *net, struct nlattr *nla,
goto out_free_ex;
}
nparms->tcfp_off_max_hint = 0;
nparms->tcfp_flags = parm->flags;
nparms->tcfp_nkeys = parm->nkeys;
@@ -268,14 +269,6 @@ static int tcf_pedit_init(struct net *net, struct nlattr *nla,
BITS_PER_TYPE(int) - 1,
nparms->tcfp_keys[i].shift);
/* The AT option can read a single byte, we can bound the actual
* value with uchar max.
*/
cur += (0xff & offmask) >> nparms->tcfp_keys[i].shift;
/* Each key touches 4 bytes starting from the computed offset */
nparms->tcfp_off_max_hint =
max(nparms->tcfp_off_max_hint, cur + 4);
}
p = to_pedit(*a);
@@ -318,15 +311,12 @@ static void tcf_pedit_cleanup(struct tc_action *a)
call_rcu(&parms->rcu, tcf_pedit_cleanup_rcu);
}
static bool offset_valid(struct sk_buff *skb, int offset)
static bool offset_valid(struct sk_buff *skb, int offset, int len)
{
if (offset > 0 && offset > skb->len)
if (offset < -(int)skb_headroom(skb))
return false;
if (offset < 0 && -offset > skb_headroom(skb))
return false;
return true;
return offset <= (int)skb->len - len;
}
static int pedit_l4_skb_offset(struct sk_buff *skb, int *hoffset, const int header_type)
@@ -393,18 +383,10 @@ TC_INDIRECT_SCOPE int tcf_pedit_act(struct sk_buff *skb,
struct tcf_pedit_key_ex *tkey_ex;
struct tcf_pedit_parms *parms;
struct tc_pedit_key *tkey;
u32 max_offset;
int i;
parms = rcu_dereference_bh(p->parms);
max_offset = (skb_transport_header_was_set(skb) ?
skb_transport_offset(skb) :
skb_network_offset(skb)) +
parms->tcfp_off_max_hint;
if (skb_ensure_writable(skb, min(skb->len, max_offset)))
goto done;
tcf_lastuse_update(&p->tcf_tm);
tcf_action_update_bstats(&p->common, skb);
@@ -412,10 +394,11 @@ TC_INDIRECT_SCOPE int tcf_pedit_act(struct sk_buff *skb,
tkey_ex = parms->tcfp_keys_ex;
for (i = parms->tcfp_nkeys; i > 0; i--, tkey++) {
int write_offset, write_len;
int offset = tkey->off;
int hoffset = 0;
u32 *ptr, hdata;
u32 val;
u32 cur_val, val;
u32 *ptr;
int rc;
if (tkey_ex) {
@@ -433,13 +416,15 @@ TC_INDIRECT_SCOPE int tcf_pedit_act(struct sk_buff *skb,
if (tkey->offmask) {
u8 *d, _d;
int at_offset;
if (!offset_valid(skb, hoffset + tkey->at)) {
if (check_add_overflow(hoffset, (int)tkey->at, &at_offset) ||
!offset_valid(skb, at_offset, sizeof(_d))) {
pr_info_ratelimited("tc action pedit 'at' offset %d out of bounds\n",
hoffset + tkey->at);
goto bad;
}
d = skb_header_pointer(skb, hoffset + tkey->at,
d = skb_header_pointer(skb, at_offset,
sizeof(_d), &_d);
if (!d)
goto bad;
@@ -451,31 +436,51 @@ TC_INDIRECT_SCOPE int tcf_pedit_act(struct sk_buff *skb,
}
}
if (!offset_valid(skb, hoffset + offset)) {
pr_info_ratelimited("tc action pedit offset %d out of bounds\n", hoffset + offset);
if (check_add_overflow(hoffset, offset, &write_offset)) {
pr_info_ratelimited("tc action pedit offset overflow\n");
goto bad;
}
ptr = skb_header_pointer(skb, hoffset + offset,
sizeof(hdata), &hdata);
if (!ptr)
if (!offset_valid(skb, write_offset, sizeof(*ptr))) {
pr_info_ratelimited("tc action pedit offset %d out of bounds\n",
write_offset);
goto bad;
}
if (write_offset < 0) {
if (skb_cow(skb, -write_offset))
goto bad;
if (write_offset + (int)sizeof(*ptr) > 0) {
if (skb_ensure_writable(skb,
min_t(int, skb->len,
write_offset + (int)sizeof(*ptr))))
goto bad;
}
} else {
if (check_add_overflow(write_offset, (int)sizeof(*ptr),
&write_len))
goto bad;
if (skb_ensure_writable(skb, min_t(int, skb->len,
write_len)))
goto bad;
}
ptr = (u32 *)(skb->data + write_offset);
cur_val = get_unaligned(ptr);
/* just do it, baby */
switch (cmd) {
case TCA_PEDIT_KEY_EX_CMD_SET:
val = tkey->val;
break;
case TCA_PEDIT_KEY_EX_CMD_ADD:
val = (*ptr + tkey->val) & ~tkey->mask;
val = (cur_val + tkey->val) & ~tkey->mask;
break;
default:
pr_info_ratelimited("tc action pedit bad command (%d)\n", cmd);
goto bad;
}
*ptr = ((*ptr & tkey->mask) ^ val);
if (ptr == &hdata)
skb_store_bits(skb, hoffset + offset, ptr, 4);
put_unaligned((cur_val & tkey->mask) ^ val, ptr);
}
goto done;