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([2405:201:31:d869:6873:3448:fe16:68a6]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7b9250cd5f6sm5941807b3a.16.2025.11.14.11.37.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Nov 2025 11:37:44 -0800 (PST) From: ssrane_b23@ee.vjti.ac.in X-Google-Original-From: ssranevjti@gmail.com To: willy@infradead.org Cc: akpm@linux-foundation.org, shakeel.butt@linux.dev, eddyz87@gmail.com, andrii@kernel.org, ast@kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linux.dev, skhan@linuxfoundation.org, david.hunter.linux@gmail.com, khalid@kernel.org, Shaurya Rane , syzbot+09b7d050e4806540153d@syzkaller.appspotmail.com Subject: [PATCH] mm/filemap: fix NULL pointer dereference in do_read_cache_folio() Date: Sat, 15 Nov 2025 01:07:29 +0530 Message-Id: <20251114193729.251892-1-ssranevjti@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Shaurya Rane When read_cache_folio() is called with a NULL filler function on a mapping that does not implement read_folio, a NULL pointer dereference occurs in filemap_read_folio(). The crash occurs when: build_id_parse() is called on a VMA backed by a file from a filesystem that does not implement ->read_folio() (e.g. procfs, sysfs, or other virtual filesystems). read_cache_folio() is called with filler =3D NULL. do_read_cache_folio() assigns filler =3D mapping->a_ops->read_folio, which is still NULL. filemap_read_folio() calls filler(), causing a NULL pointer dereference. The fix is to add a NULL check after the fallback assignment and return -EIO. Callers handle this error safely. Reported-by: syzbot+09b7d050e4806540153d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D09b7d050e4806540153d Fixes: ad41251c290d ("lib/buildid: implement sleepable build_id_parse() API= ") Signed-off-by: Shaurya Rane --- mm/filemap.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index 13f0259d993c..f700fe931d61 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3980,6 +3980,8 @@ static struct folio *do_read_cache_folio(struct addre= ss_space *mapping, =20 if (!filler) filler =3D mapping->a_ops->read_folio; + if (!filler) + return ERR_PTR(-EIO); repeat: folio =3D filemap_get_folio(mapping, index); if (IS_ERR(folio)) { --=20 2.34.1