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([2409:40c0:1035:4e2d:eebe:9df9:70d0:b210]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-bc36ed72cd1sm8509995a12.11.2025.11.15.21.42.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 15 Nov 2025 21:42:18 -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, syzbot+09b7d050e4806540153d@syzkaller.appspotmail.com, ssrane_b23@ee.vjti.ac.in Subject: [PATCH v2] mm/filemap: fix NULL pointer dereference in do_read_cache_folio() Date: Sun, 16 Nov 2025 11:12:05 +0530 Message-Id: <20251116054205.114412-1-ssranevjti@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: qpbuzzsbe9d64ccdixnmdrrqutbhdmec X-Rspam-User: X-Rspamd-Queue-Id: 541D8120004 X-Rspamd-Server: rspam10 X-HE-Tag: 1763271740-750024 X-HE-Meta: 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 UXjA+4JM 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 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: From: Shaurya Rane When read_cache_folio() is called with a NULL filler function on a mapping that doesn't implement read_folio, a NULL pointer dereference occurs in filemap_read_folio(). The crash occurs when: 1. build_id_parse() is called on a VMA backed by a file from a filesystem that doesn't implement address_space_operations.read_folio (e.g., procfs, sysfs, or other virtual filesystems) 2. read_cache_folio() is called with filler=NULL 3. do_read_cache_folio() sets filler = mapping->a_ops->read_folio (still NULL) 4. 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, which is handled gracefully by the callers. Reported-by: syzbot+09b7d050e4806540153d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=09b7d050e4806540153d Fixes: ad41251c290d ("lib/buildid: implement sleepable build_id_parse() API") Signed-off-by: Shaurya Rane --- Changes in v2: - Add early read_folio check in __build_id_parse() for unsupported filesystems. -Add defensive !filler check in do_read_cache_folio() to prevent NULL dereference. --- lib/buildid.c | 3 +++ mm/filemap.c | 2 ++ 2 files changed, 5 insertions(+) diff --git a/lib/buildid.c b/lib/buildid.c index c4b0f376fb34..3136cc92010f 100644 --- a/lib/buildid.c +++ b/lib/buildid.c @@ -298,6 +298,9 @@ static int __build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, /* only works for page backed storage */ if (!vma->vm_file) return -EINVAL; + /* check if filesystem supports page cache operations */ + if (!vma->vm_file->f_mapping->a_ops->read_folio) + return -EINVAL; freader_init_from_file(&r, buf, sizeof(buf), vma->vm_file, may_fault); 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 address_space *mapping, if (!filler) filler = mapping->a_ops->read_folio; + if (!filler) + return ERR_PTR(-EIO); repeat: folio = filemap_get_folio(mapping, index); if (IS_ERR(folio)) { -- 2.34.1