Date: Tue, 17 Oct 2023 13:37:07 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 761ae1ce798a - main - ktrace: Handle uio_resid underflow via MSG_TRUNC Message-ID: <202310171337.39HDb76r095780@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=761ae1ce798add862d78728cc5ac5240ce7db779 commit 761ae1ce798add862d78728cc5ac5240ce7db779 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2023-10-16 20:11:55 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2023-10-17 13:12:19 +0000 ktrace: Handle uio_resid underflow via MSG_TRUNC When recvmsg(2) is used with MSG_TRUNC on an atomic socket type (DGRAM or SEQPACKET), soreceive_generic() and uipc_peek_dgram() may intentionally underflow uio_resid so that userspace can find out how many bytes it should have asked for. If this happens, and KTR_GENIO is enabled, ktrgenio() will attempt to copy in beyond the end of the output buffer's iovec. In general this will silently cause the ktrace operation to fail since it'll result in EFAULT from uiomove(). Let's be more careful and make sure not to try and copy more bytes than we have. Fixes: be1f485d7d6b ("sockets: add MSG_TRUNC flag handling for recvfrom()/recvmsg().") Reported by: syzbot+30b4bb0c0bc0f53ac198@syzkaller.appspotmail.com Reviewed by: kib MFC after: 3 days Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D42099 --- sys/kern/uipc_syscalls.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/sys/kern/uipc_syscalls.c b/sys/kern/uipc_syscalls.c index 2dad9d487290..c7c2e6544902 100644 --- a/sys/kern/uipc_syscalls.c +++ b/sys/kern/uipc_syscalls.c @@ -948,7 +948,8 @@ kern_recvit(struct thread *td, int s, struct msghdr *mp, enum uio_seg fromseg, AUDIT_ARG_SOCKADDR(td, AT_FDCWD, fromsa); #ifdef KTRACE if (ktruio != NULL) { - ktruio->uio_resid = len - auio.uio_resid; + /* MSG_TRUNC can trigger underflow of uio_resid. */ + ktruio->uio_resid = MIN(len - auio.uio_resid, len); ktrgenio(s, UIO_READ, ktruio, error); } #endif
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