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Paul Chaignon fe9d33f047 bpf: Explicitly check accesses to bpf_sock_addr 
[ Upstream commit 6fabca2fc9 ]

Syzkaller found a kernel warning on the following sock_addr program:

    0: r0 = 0
    1: r2 = *(u32 *)(r1 +60)
    2: exit

which triggers:

    verifier bug: error during ctx access conversion (0)

This is happening because offset 60 in bpf_sock_addr corresponds to an
implicit padding of 4 bytes, right after msg_src_ip4. Access to this
padding isn't rejected in sock_addr_is_valid_access and it thus later
fails to convert the access.

This patch fixes it by explicitly checking the various fields of
bpf_sock_addr in sock_addr_is_valid_access.

I checked the other ctx structures and is_valid_access functions and
didn't find any other similar cases. Other cases of (properly handled)
padding are covered in new tests in a subsequent patch.

Fixes: 1cedee13d2 ("bpf: Hooks for sys_sendmsg")
Reported-by: syzbot+136ca59d411f92e821b7@syzkaller.appspotmail.com
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Closes: https://syzkaller.appspot.com/bug?extid=136ca59d411f92e821b7
Link: https://lore.kernel.org/bpf/b58609d9490649e76e584b0361da0abd3c2c1779.1758094761.git.paul.chaignon@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-10-15 12:00:02 +02:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.