4.9-stable review patch. If anyone has any objections, please let me know.
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From: Jiri Slaby jslaby@suse.cz
commit fc3dc67471461c0efcb1ed22fb7595121d65fad9 upstream.
fcntl(0, F_SETOWN, 0x80000000) triggers: UBSAN: Undefined behaviour in fs/fcntl.c:118:7 negation of -2147483648 cannot be represented in type 'int': CPU: 1 PID: 18261 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1 ... Call Trace: ... [<ffffffffad8f0868>] ? f_setown+0x1d8/0x200 [<ffffffffad8f19a9>] ? SyS_fcntl+0x999/0xf30 [<ffffffffaed1fb00>] ? entry_SYSCALL_64_fastpath+0x23/0xc1
Fix that by checking the arg parameter properly (against INT_MAX) before "who = -who". And return immediatelly with -EINVAL in case it is wrong. Note that according to POSIX we can return EINVAL: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fcntl.html
[EINVAL] The cmd argument is F_SETOWN and the value of the argument is not valid as a process or process group identifier.
[v2] returns an error, v1 used to fail silently [v3] implement proper check for the bad value INT_MIN
Signed-off-by: Jiri Slaby jslaby@suse.cz Cc: Jeff Layton jlayton@poochiereds.net Cc: "J. Bruce Fields" bfields@fieldses.org Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Jeff Layton jlayton@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/fcntl.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -114,6 +114,10 @@ void f_setown(struct file *filp, unsigne int who = arg; type = PIDTYPE_PID; if (who < 0) { + /* avoid overflow below */ + if (who == INT_MIN) + return; + type = PIDTYPE_PGID; who = -who; }