[PATCH v2 0/3] daemon: fix network address handling bugs

Fix three related issues in daemon.c's network address handling:

IPv6 address corruption in lookup_hostname(): getaddrinfo() is called with AF_UNSPEC hints, so it may return IPv6 results. However, the code unconditionally casts ai_addr to sockaddr_in and passes AF_INET to inet_ntop(). On IPv6-only hosts, this reads from the wrong struct offset, producing garbage IP addresses. Fixed by checking ai_family and handling both AF_INET and AF_INET6.

IPv6 address truncation in ip2str(): The sockaddr struct size (ai_addrlen) is passed as the output buffer size to inet_ntop(). For IPv6, sizeof(sockaddr_in6) is 28 bytes but INET6_ADDRSTRLEN is 46, so long IPv6 addresses are silently truncated. Fixed by passing sizeof(ip) instead, and dropping the now-unused len parameter.

NULL pointer in execute() logging: REMOTE_PORT environment variable is used in a format string without a NULL check (only REMOTE_ADDR was checked). If REMOTE_PORT is unset, NULL is passed to printf's %s, which is undefined behavior. Fixed by using a fallback string.

Changes since v1:

 * Split the single patch into three separate commits, one per fix, per
   Patrick's review.
 * Deduplicated the address family handling in lookup_hostname(): instead of
   duplicating the inet_ntop() call for each family, the address pointer is
   extracted into a local void *addr variable first, then inet_ntop() is
   called once, per Patrick's suggestion.
 * The (void *) intermediate cast on ai_addr is used intentionally: C
   guarantees any object pointer round-trips safely through void *, and it
   keeps the per-family blocks shorter than spelling out the full struct
   casts.
 * For the REMOTE_PORT NULL guard: both REMOTE_ADDR and REMOTE_PORT are set
   by the same code path in handle(), so neither should be NULL
   independently. The guard makes the code consistent with the existing
   REMOTE_ADDR check and avoids undefined behavior from printf %s with a
   NULL argument.
 * Die on unexpected address families in lookup_hostname() rather than
   silently leaving addrbuf uninitialized.

Sebastien Tardif (3):
  daemon: fix IPv6 address corruption in lookup_hostname()
  daemon: fix IPv6 address truncation in ip2str()
  daemon: guard NULL REMOTE_PORT in execute() logging

 daemon.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

base-commit: 59ff4886a579f4bc91e976fe18590b9ae02c7a08
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2300%2FSebTardif%2Ffix%2Fdaemon-ipv6-and-null-port-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2300/SebTardif/fix/daemon-ipv6-and-null-port-v2
Pull-Request: https://github.com/git/git/pull/2300

Range-diff vs v1:

 1:  b2d8143811 = 1:  b2d8143811 daemon: fix IPv6 address corruption in lookup_hostname()
 2:  5c01ec3cad = 2:  5c01ec3cad daemon: fix IPv6 address truncation in ip2str()
 3:  1b2f9d1a07 ! 3:  e312735716 daemon: guard NULL REMOTE_PORT in execute() logging
     @@ Metadata
       ## Commit message ##
          daemon: guard NULL REMOTE_PORT in execute() logging
      
     -    The REMOTE_PORT environment variable is used in a format string
     -    without a NULL check, while REMOTE_ADDR is checked. If REMOTE_PORT
     -    is unset, NULL is passed to printf's %s, which is undefined behavior.
     +    REMOTE_ADDR and REMOTE_PORT are both set by the same code path in
     +    handle(), so neither should be NULL independently. However, the
     +    existing code checks REMOTE_ADDR before the loginfo() call but not
     +    REMOTE_PORT. If REMOTE_PORT were unset, NULL would be passed to
     +    printf's %s, which is undefined behavior.
      
     -    Add a fallback string for the NULL case.
     +    Add a fallback string for the NULL case, matching the existing
     +    REMOTE_ADDR guard for consistency.
      
          Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>