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Miller" , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , netdev@vger.kernel.org, eric.dumazet@gmail.com, Eric Dumazet , syzbot+53ecc09fb81df10ef4de@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" vcc_setsockopt() contained an ineffective optlen check: if (__SO_LEVEL_MATCH(optname, level) && optlen != __SO_SIZE(optname)) return -EINVAL; If __SO_LEVEL_MATCH(optname, level) evaluated to false (e.g. if the caller passed a mismatched level), the length check optlen != __SO_SIZE(optname) was short-circuited and bypassed. Execution then fell through to switch(optname), calling copy_from_sockptr() assuming optval contained sufficient space. Furthermore, even if level matched, a cgroup BPF setsockopt filter could shrink optlen after entry. Because copy_from_sockptr() on kernel pointers uses memcpy(), this leads to a KASAN slab-out-of-bounds read when optlen is smaller than the expected structure size. Fix this by using copy_safe_from_sockptr(), which unconditionally validates that optlen is at least the expected size before copying. Also change the local 'value' variable type from 'unsigned long' to 'int' so that SO_SETCLP matches its sizeof(int) ABI encoding on 64-bit systems. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+53ecc09fb81df10ef4de@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=53ecc09fb81df10ef4de Signed-off-by: Eric Dumazet --- v2: change @value type to "int" v1: https://lore.kernel.org/netdev/20260804145806.2112004-1-edumazet@google.com/T/#u net/atm/common.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/net/atm/common.c b/net/atm/common.c index c7f92405daf050ecd2a507e41efdd622ab8dc6a8..81195727fa18ba4e6146c0c02cd3898d17fc436f 100644 --- a/net/atm/common.c +++ b/net/atm/common.c @@ -710,7 +710,7 @@ int vcc_setsockopt(struct socket *sock, int level, int optname, sockptr_t optval, unsigned int optlen) { struct atm_vcc *vcc; - unsigned long value; + int value; int error; if (__SO_LEVEL_MATCH(optname, level) && optlen != __SO_SIZE(optname)) @@ -722,8 +722,10 @@ int vcc_setsockopt(struct socket *sock, int level, int optname, { struct atm_qos qos; - if (copy_from_sockptr(&qos, optval, sizeof(qos))) - return -EFAULT; + error = copy_safe_from_sockptr(&qos, sizeof(qos), optval, + optlen); + if (error) + return error; error = check_qos(&qos); if (error) return error; @@ -737,8 +739,10 @@ int vcc_setsockopt(struct socket *sock, int level, int optname, return 0; } case SO_SETCLP: - if (copy_from_sockptr(&value, optval, sizeof(value))) - return -EFAULT; + error = copy_safe_from_sockptr(&value, sizeof(value), optval, + optlen); + if (error) + return error; if (value) vcc->atm_options |= ATM_ATMOPT_CLP; else -- 2.55.0.571.g244d577d93-goog