[PATCH net] net/sched: cls_flower: validate mask pointer after nla_next()

From: Aohan Mei <redacted>

fl_set_enc_opt() iterates the key's nested tunnel-option attributes
with nla_for_each_attr() while advancing a single mask pointer via
nla_next() at the bottom of each loop, so the mask cursor is driven
by the number of key attributes rather than by the mask's own
attributes.  The nla_ok() added by commit c96adff956191 ("cls_flower:
call nla_ok() before nla_next()") only validates the mask pointer
that was just consumed; the pointer produced by nla_next() is used by
the next iteration (fl_set_geneve_opt() and siblings) without any
validation.

The mask's nested attributes are validated with NL_VALIDATE_LIBERAL,
which merely warns on trailing bytes that do not form a complete
attribute.  A mask carrying one valid attribute plus 1-3 residue
bytes (or a non-aligned attribute length making msk_depth negative)
therefore reaches the next iteration with msk_depth != 0, so neither
the !msk_depth check in fl_set_enc_opt() nor the !depth check in the
per-type helpers fires.  nla_type() then reads past the mask payload
and nla_parse_nested_deprecated() iterates with an nla_len taken
from those bytes, reading well beyond the mask attribute (KASAN:
slab-out-of-bounds read in __nla_validate_parse from fl_change()).

Validate the advanced mask pointer as well: when the mask is not
legitimately exhausted (msk_depth != 0) and the new pointer fails
nla_ok(), reject the filter with -EINVAL.  An exactly exhausted mask
still skips the check, preserving exact-match behaviour for the
remaining key attributes.

Fixes: c96adff95619 ("cls_flower: call nla_ok() before nla_next()")
Reported-by: TencentOS Corvus AI <redacted>
Cc: stable@vger.kernel.org
Assisted-by: CodeBuddy:Kimi-K3
Signed-off-by: Aohan Mei <redacted>
---
 net/sched/cls_flower.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index 0e275b58151c..1cefea571efd 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c

@@ -1703,6 +1703,11 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
 			return -EINVAL;
 		}
 		nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
+
+		if (msk_depth && !nla_ok(nla_opt_msk, msk_depth)) {
+			NL_SET_ERR_MSG(extack, "A mask attribute is invalid");
+			return -EINVAL;
+		}
 	}
 
 	return 0;

-- 
2.43.7