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Sun, 02 Aug 2026 21:34:36 -0700 (PDT) From: Yuejie Shi To: Konstantin Komarov Cc: ntfs3@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH] fs/ntfs3: validate the EA value length in ntfs_read_ea() Date: Mon, 3 Aug 2026 12:34:32 +0800 Message-ID: <20260803043432.94886-1-syjcnss@gmail.com> X-Mailer: git-send-email 2.50.1 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" ntfs_read_ea() checks the $EA list for consistency, but it only recomputes the packed size of an entry when the entry's own size field is zero: for (off =3D 0; off < size; off +=3D ea_size) { const struct EA_FULL *ef =3D Add2Ptr(ea_p, off); u32 bytes =3D size - off; ... if (ef->size) { ea_size =3D le32_to_cpu(ef->size); if (ea_size > bytes) goto out1; continue; /* <- elength never checked */ } ... ea_size =3D ALIGN(struct_size(ef, name, 1 + ef->name_len + le16_to_cpu(ef->elength)), 4); if (ea_size > bytes) goto out1; } ef->size is non-zero for every entry except the last one, and it is what ntfs3 itself writes (ntfs_set_ea() stores exactly that aligned packed size), so in practice elength is not validated at all. find_ea() then uses unpacked_ea_size(), which also prefers ea->size when it is set, so it agrees and hands the entry back. ntfs_get_ea() copies elength bytes with no further bound of its own: len =3D le16_to_cpu(ea->elength); ... if (len > size) { /* size is the *caller's* buffer */ err =3D -ERANGE; ... } memcpy(buffer, ea->name + ea->name_len + 1, len); so a caller that supplies a large enough buffer receives up to 64 KiB of whatever follows the small $EA allocation -- straight to userspace via getxattr(2). Compute the packed size unconditionally and require it to fit in the entry. Hoist the "bytes < offsetof(struct EA_FULL, name)" test above the ef->size branch as well: name_len and elength were being read there without it, which is itself a small over-read of the kmalloc'd buffer when fewer than 8 bytes are left. The old "bytes < sizeof(ef->size)" test is subsumed by it. # mkntfs image; create /mnt/ntfs/poc with user.ntfs6 set, then rewrite # that EA_FULL's elength from 0xf to 0xff00 on the raw device mount -t ntfs3 -o ro /dev/vda /mnt/ntfs getxattr("/mnt/ntfs/poc", "user.ntfs6", buf, 128 * 1024); BUG: KASAN: slab-out-of-bounds in ntfs_get_ea+0x294/0x3e0 Read of size 65280 at addr ffff0000cca53acf by task xattr_probe/142 __asan_memcpy+0x3c/0xa0 ntfs_get_ea+0x294/0x3e0 ntfs_getxattr+0x284/0x318 __vfs_getxattr+0x104/0x160 vfs_getxattr+0x1b4/0x1e0 do_getxattr+0xcc/0x230 path_getxattrat+0x184/0x270 __arm64_sys_getxattr+0x64/0x80 Allocated by task 142: __kmalloc_noprof+0x294/0x668 ntfs_read_ea+0x1e4/0x420 ntfs_get_ea+0x2c8/0x3e0 The buggy address belongs to the object at ffff0000cca53a80 which belongs to the cache kmalloc-96 of size 96 The object being over-read is the one ntfs_read_ea() just allocated, and it is 96 bytes. Entries written by ntfs3 and by Windows set size to the aligned packed size, so the new test does not reject anything a working filesystem produces. Fixes: be71b5cba2e6 ("fs/ntfs3: Add attrib operations") Cc: stable@vger.kernel.org Signed-off-by: Yuejie Shi --- fs/ntfs3/xattr.c | 27 ++++++++++++++++----------- 1 file changed, 16 insertions(+), 11 deletions(-) diff --git a/fs/ntfs3/xattr.c b/fs/ntfs3/xattr.c index 04814dd29375..e67a1100d0cd 100644 --- a/fs/ntfs3/xattr.c +++ b/fs/ntfs3/xattr.c @@ -146,26 +146,31 @@ static int ntfs_read_ea(struct ntfs_inode *ni, struct=20 for (off =3D 0; off < size; off +=3D ea_size) { const struct EA_FULL *ef =3D Add2Ptr(ea_p, off); u32 bytes =3D size - off; + u32 packed_size; =20 - /* Check if we can use field ea->size. */ - if (bytes < sizeof(ef->size)) + /* Check if we can use fields ef->name_len and ef->elength. */ + if (bytes < offsetof(struct EA_FULL, name)) goto out1; =20 + /* + * The name and the value have to fit in the entry whether or + * not ef->size is set, because ntfs_get_ea() copies elength + * bytes out of this buffer and checks them only against the + * caller supplied buffer size. + */ + packed_size =3D ALIGN(struct_size(ef, name, + 1 + ef->name_len + + le16_to_cpu(ef->elength)), + 4); + if (ef->size) { ea_size =3D le32_to_cpu(ef->size); - if (ea_size > bytes) + if (ea_size > bytes || packed_size > ea_size) goto out1; continue; } =20 - /* Check if we can use fields ef->name_len and ef->elength. */ - if (bytes < offsetof(struct EA_FULL, name)) - goto out1; - - ea_size =3D ALIGN(struct_size(ef, name, - 1 + ef->name_len + - le16_to_cpu(ef->elength)), - 4); + ea_size =3D packed_size; if (ea_size > bytes) goto out1; } -- 2.51.0