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From: Shakeel Butt Date: Thu, 29 Jan 2026 20:40:51 -0800 X-Gmail-Original-Message-ID: X-Gm-Features: AZwV_Qg5dfk2ht8JupIDFXTqsdxMg36LioUN_5yZDOZCUGFX3Rv7JHpElpOR8RI Message-ID: Subject: Re: [PATCH v2 mm-stable] procfs: avoid fetching build ID while holding VMA lock To: Andrii Nakryiko Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, surenb@google.com, syzbot+4e70c8e0a2017b432f7a@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: C232220004 X-Stat-Signature: y4as8hk9qqaqrhzb7pu6faruk4zpcr7p X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1769748072-721716 X-HE-Meta: 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 Md/QIQDK DSjK0ek//TXXm35JUMSSAthj4pdUDPsC1LF2Sm0J8FFZ/9EdESPmeDzLfrpFk8VSDvxrNW82ohkCEm/Q0vfkCv039gKYpK84WEzWYzL7YkDJ4EKKtfY4dl2RyZF3MtZAmTDe8cnvY7X5uWsGGCkdIVE/fybstID6yN2FbEWg9G6KZ8UQRipXw59SHJ6folETFHNFkJCSC401M8IIz6A419KGNccxUf6Qzxqe1Qoqz5jre2uBWBJxgisjPz9QAZeBwdPKWv04REgwpME8XGELAA/Tso3nNxKqFeicLRwutEAiBEUtBEZw0sP35UxZXf13eZuJEdyLGilpcy3H3czM+eCONUjnPIpfZTd6Sppc7UeXkAbRdxoenVstInw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jan 29, 2026 at 1:53=E2=80=AFPM Andrii Nakryiko = wrote: > > Fix PROCMAP_QUERY to fetch optional build ID only after dropping mmap_loc= k or > per-VMA lock, whichever was used to lock VMA under question, to avoid dea= dlock > reported by syzbot: > > -> #1 (&mm->mmap_lock){++++}-{4:4}: > __might_fault+0xed/0x170 > _copy_to_iter+0x118/0x1720 > copy_page_to_iter+0x12d/0x1e0 > filemap_read+0x720/0x10a0 > blkdev_read_iter+0x2b5/0x4e0 > vfs_read+0x7f4/0xae0 > ksys_read+0x12a/0x250 > do_syscall_64+0xcb/0xf80 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > -> #0 (&sb->s_type->i_mutex_key#8){++++}-{4:4}: > __lock_acquire+0x1509/0x26d0 > lock_acquire+0x185/0x340 > down_read+0x98/0x490 > blkdev_read_iter+0x2a7/0x4e0 > __kernel_read+0x39a/0xa90 > freader_fetch+0x1d5/0xa80 > __build_id_parse.isra.0+0xea/0x6a0 > do_procmap_query+0xd75/0x1050 > procfs_procmap_ioctl+0x7a/0xb0 > __x64_sys_ioctl+0x18e/0x210 > do_syscall_64+0xcb/0xf80 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > rlock(&mm->mmap_lock); > lock(&sb->s_type->i_mutex_key#8); > lock(&mm->mmap_lock); > rlock(&sb->s_type->i_mutex_key#8); > > *** DEADLOCK *** > > To make this safe, we need to grab file refcount while VMA is still locke= d, but > other than that everything is pretty straightforward. Internal build_id_p= arse() > API assumes VMA is passed, but it only needs the underlying file referenc= e, so > just add another variant build_id_parse_file() that expects file passed > directly. > > Fixes: ed5d583a88a9 ("fs/procfs: implement efficient VMA querying API for= /proc//maps") > Reported-by: syzbot+4e70c8e0a2017b432f7a@syzkaller.appspotmail.com > Reviewed-by: Suren Baghdasaryan > Tested-by: Suren Baghdasaryan > Signed-off-by: Andrii Nakryiko Reviewed-by: Shakeel Butt