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Sat, 30 May 2026 01:07:12 -0700 (PDT) From: Jamal Hadi Salim To: netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, jiri@resnulli.us, victor@mojatatu.com, david.laight.linux@gmail.com, yimingqian591@gmail.com, keenanat2000@gmail.com, 2045gemini@gmail.com, rollkingzzc@gmail.com, toke@redhat.com, dcaratti@redhat.com, security@kernel.org, linux-kernel@vger.kernel.org, Rajat Gupta , Jamal Hadi Salim Subject: [PATCH net v4 1/1] net/sched: fix pedit partial COW leading to page cache corruption Date: Sat, 30 May 2026 04:06:43 -0400 Message-Id: <20260530080643.1345521-1-jhs@mojatatu.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Rajat Gupta 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: 8b796475fd78 ("net/sched: act_pedit: really ensure the skb is writable") Reported-by: Yiming Qian Reported-by: Keenan Dong Reported-by: Han Guidong <2045gemini@gmail.com> Reported-by: Zhang Cen Reviewed-by: Han Guidong <2045gemini@gmail.com> Tested-by: Han Guidong <2045gemini@gmail.com> Reviewed-by: Davide Caratti Tested-by: Davide Caratti Reviewed-by: Toke Høiland-Jørgensen Tested-by: Toke Høiland-Jørgensen Reviewed-by: Victor Nogueira Tested-by: Victor Nogueira Acked-by: Jamal Hadi Salim Signed-off-by: Rajat Gupta --- v3->v4 1) Restore the Fixes tag which was accidentally deleted in v3 2) Remove tcfp_off_max_hint as pointed by sashiko [1] 3) Fix a boundary condition identified by sashiko [1] 4) Add unaligned access support to safely access ptr support to compensate for removal of skb_header_pointer() / skb_store_bits() which handled it fine [1]https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260527181731.1166373-1-jhs%40mojatatu.com --- include/net/tc_act/tc_pedit.h | 1 - net/sched/act_pedit.c | 72 ++++++++++++++++++++--------------- 2 files changed, 41 insertions(+), 32 deletions(-) diff --git a/include/net/tc_act/tc_pedit.h b/include/net/tc_act/tc_pedit.h index f58ee15cd858..cb7b82f2cbc7 100644 --- a/include/net/tc_act/tc_pedit.h +++ b/include/net/tc_act/tc_pedit.h @@ -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; diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c index bc20f08a2789..4e60793d184a 100644 --- a/net/sched/act_pedit.c +++ b/net/sched/act_pedit.c @@ -16,6 +16,8 @@ #include #include #include +#include +#include #include #include #include @@ -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; @@ -273,9 +274,6 @@ static int tcf_pedit_init(struct net *net, struct nlattr *nla, */ 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 +316,12 @@ 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 +388,10 @@ 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 +399,11 @@ 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 +421,15 @@ 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, 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 +441,51 @@ 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(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; -- 2.34.1