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net: preserve socketpair output on setup failure

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socketpair() writes the reserved descriptor numbers to userspace before
creating the sockets and their file objects. A later failure therefore
leaves a modified caller's array despite returning an error, contrary to
POSIX. For example, socketpair(AF_UNIX, SOCK_STREAM, -1, fd) returns
EPROTONOSUPPORT but replaces the array's sentinel values with unused fd
numbers.

Defer the output stores until both file objects have been created, before
installing either descriptor. If a store faults, drop both file references
before releasing the reserved descriptor slots. Keep the early descriptor
reservation and the existing setup-failure cleanup paths.

In practice, I doubt anyone notices. But this aligns with the expected
behavior

Signed-off-by: Steve Grubb <sgrubb@redhat.com>
Link: https://patch.msgid.link/JyK226D0S5CWGUpAC4MO4A@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Steve Grubb 2026-09-10 13:53:15 -04:00 committed by Jakub Kicinski
parent c5faf1d4df
commit 65734bbe4a
1 changed files with 11 additions and 12 deletions
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23
net/socket.c
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@ -1851,10 +1851,7 @@ int __sys_socketpair(int family, int type, int protocol, int __user *usockvec)
if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))
flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;
/*
* reserve descriptors and make sure we won't fail
* to return them to userland.
*/
/* Reserve both descriptors before creating the sockets. */
fd1 = get_unused_fd_flags(flags);
if (unlikely(fd1 < 0))
return fd1;
@ -1865,14 +1862,6 @@ int __sys_socketpair(int family, int type, int protocol, int __user *usockvec)
return fd2;
}
err = put_user(fd1, &usockvec[0]);
if (err)
goto out;
err = put_user(fd2, &usockvec[1]);
if (err)
goto out;
/*
* Obtain the first socket and check if the underlying protocol
* supports the socketpair call.
@ -1916,6 +1905,16 @@ int __sys_socketpair(int family, int type, int protocol, int __user *usockvec)
goto out;
}
/* Publish the descriptors now that it shouldn't fail. */
err = put_user(fd1, &usockvec[0]);
if (!err)
err = put_user(fd2, &usockvec[1]);
if (err) {
fput(newfile2);
fput(newfile1);
goto out;
}
audit_fd_pair(fd1, fd2);
fd_install(fd1, newfile1);