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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2df378440f4sm7398615ad.59.2026.09.19.15.26.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 15:26:07 -0700 (PDT) From: Hui Peng To: brauner@kernel.org, jack@suse.cz Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] romfs: reject non-advancing nextfh offsets in romfs_lookup() and romfs_readdir() Date: Sat, 19 Sep 2026 22:26:07 +0000 Message-ID: <20260919222607.3794829-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In romfs_lookup() and romfs_readdir() (fs/romfs/super.c), verify that the masked nextfh offset strictly advances (or is 0 to terminate the directory) so a self-referential or backward nextfh link in a corrupted RomFS image cannot cause an infinite loop in the kernel. Fixes: da4458bda237 ("NOMMU: Make it possible for RomFS to use MTD devices directly") Assisted-by: LLM Signed-off-by: Hui Peng --- diff --git a/fs/romfs/super.c b/fs/romfs/super.c index 7f783d6173e8..4d787ee06d4a 100644 --- a/fs/romfs/super.c +++ b/fs/romfs/super.c @@ -191,6 +191,8 @@ static int romfs_readdir(struct file *file, struct dir_context *ctx) romfs_dtype_table[nextfh & ROMFH_TYPE])) goto out; + if ((nextfh & ROMFH_MASK) && (nextfh & ROMFH_MASK) <= offset) + goto out; offset = nextfh & ROMFH_MASK; } out: @@ -223,6 +225,8 @@ static struct dentry *romfs_lookup(struct inode *dir, struct dentry *dentry, len = dentry->d_name.len; for (;;) { + unsigned long next_offset; + if (!offset || offset >= maxoff) break; @@ -246,7 +250,12 @@ static struct dentry *romfs_lookup(struct inode *dir, struct dentry *dentry, } /* next entry */ - offset = be32_to_cpu(ri.next) & ROMFH_MASK; + next_offset = be32_to_cpu(ri.next) & ROMFH_MASK; + if (next_offset && next_offset <= offset) { + ret = -EIO; + goto error; + } + offset = next_offset; } return d_splice_alias(inode, dentry);