sip_skip_whitespace() returns dptr unchanged when its own loop exhausts the buffer (dptr == limit), instead of NULL like its sibling sip_follow_continuation() returns on its own "no more data" path. ct_sip_get_header() only checks for NULL after calling it: dptr = sip_skip_whitespace(dptr, limit); if (dptr == NULL) break; if (*dptr != ':' || ++dptr >= limit) break; so a recognized header name followed only by spaces/tabs running to the exact end of the SIP payload, with no colon, makes the very next statement read one byte past the buffer. Make both "no more data" outcomes return NULL, matching the convention sip_follow_continuation() already uses and that both existing callers already check for. Fixes: ea45f12a2766d ("[NETFILTER]: nf_conntrack_sip: parse SIP headers properly") Signed-off-by: Joas Antonio dos Santos --- Testing: 7-byte reproducer ("\r\nTo ", no colon, buffer ends on trailing spaces) no longer crashes; 500000-run libFuzzer regression against a userspace harness linking the unmodified extracted parsing functions is clean, no behavior change on the existing corpus. Reproducer bytes available on request. net/netfilter/nf_conntrack_sip.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c index 6830c9da3..000000000 100644 --- a/net/netfilter/nf_conntrack_sip.c +++ b/net/netfilter/nf_conntrack_sip.c @@ -429,7 +429,7 @@ static const char *sip_skip_whitespace(const char *dptr, const char *limit) dptr = sip_follow_continuation(dptr, limit); break; } - return dptr; + return dptr < limit ? dptr : NULL; } /* Search within a SIP header value, dealing with continuation lines */