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    Subject[PATCH 5.10 542/599] ubifs: Fix read out-of-bounds in ubifs_wbuf_write_nolock()
    Date
    From: Zhihao Cheng <chengzhihao1@huawei.com>

    commit 4f2262a334641e05f645364d5ade1f565c85f20b upstream.

    Function ubifs_wbuf_write_nolock() may access buf out of bounds in
    following process:

    ubifs_wbuf_write_nolock():
    aligned_len = ALIGN(len, 8); // Assume len = 4089, aligned_len = 4096
    if (aligned_len <= wbuf->avail) ... // Not satisfy
    if (wbuf->used) {
    ubifs_leb_write() // Fill some data in avail wbuf
    len -= wbuf->avail; // len is still not 8-bytes aligned
    aligned_len -= wbuf->avail;
    }
    n = aligned_len >> c->max_write_shift;
    if (n) {
    n <<= c->max_write_shift;
    err = ubifs_leb_write(c, wbuf->lnum, buf + written,
    wbuf->offs, n);
    // n > len, read out of bounds less than 8(n-len) bytes
    }

    , which can be catched by KASAN:
    =========================================================
    BUG: KASAN: slab-out-of-bounds in ecc_sw_hamming_calculate+0x1dc/0x7d0
    Read of size 4 at addr ffff888105594ff8 by task kworker/u8:4/128
    Workqueue: writeback wb_workfn (flush-ubifs_0_0)
    Call Trace:
    kasan_report.cold+0x81/0x165
    nand_write_page_swecc+0xa9/0x160
    ubifs_leb_write+0xf2/0x1b0 [ubifs]
    ubifs_wbuf_write_nolock+0x421/0x12c0 [ubifs]
    write_head+0xdc/0x1c0 [ubifs]
    ubifs_jnl_write_inode+0x627/0x960 [ubifs]
    wb_workfn+0x8af/0xb80

    Function ubifs_wbuf_write_nolock() accepts that parameter 'len' is not 8
    bytes aligned, the 'len' represents the true length of buf (which is
    allocated in 'ubifs_jnl_xxx', eg. ubifs_jnl_write_inode), so
    ubifs_wbuf_write_nolock() must handle the length read from 'buf' carefully
    to write leb safely.

    Fetch a reproducer in [Link].

    Fixes: 1e51764a3c2ac0 ("UBIFS: add new flash file system")
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=214785
    Reported-by: Chengsong Ke <kechengsong@huawei.com>
    Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
    Signed-off-by: Richard Weinberger <richard@nod.at>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/ubifs/io.c | 34 ++++++++++++++++++++++++++++++----
    1 file changed, 30 insertions(+), 4 deletions(-)

    --- a/fs/ubifs/io.c
    +++ b/fs/ubifs/io.c
    @@ -846,16 +846,42 @@ int ubifs_wbuf_write_nolock(struct ubifs
    */
    n = aligned_len >> c->max_write_shift;
    if (n) {
    - n <<= c->max_write_shift;
    + int m = n - 1;
    +
    dbg_io("write %d bytes to LEB %d:%d", n, wbuf->lnum,
    wbuf->offs);
    - err = ubifs_leb_write(c, wbuf->lnum, buf + written,
    - wbuf->offs, n);
    +
    + if (m) {
    + /* '(n-1)<<c->max_write_shift < len' is always true. */
    + m <<= c->max_write_shift;
    + err = ubifs_leb_write(c, wbuf->lnum, buf + written,
    + wbuf->offs, m);
    + if (err)
    + goto out;
    + wbuf->offs += m;
    + aligned_len -= m;
    + len -= m;
    + written += m;
    + }
    +
    + /*
    + * The non-written len of buf may be less than 'n' because
    + * parameter 'len' is not 8 bytes aligned, so here we read
    + * min(len, n) bytes from buf.
    + */
    + n = 1 << c->max_write_shift;
    + memcpy(wbuf->buf, buf + written, min(len, n));
    + if (n > len) {
    + ubifs_assert(c, n - len < 8);
    + ubifs_pad(c, wbuf->buf + len, n - len);
    + }
    +
    + err = ubifs_leb_write(c, wbuf->lnum, wbuf->buf, wbuf->offs, n);
    if (err)
    goto out;
    wbuf->offs += n;
    aligned_len -= n;
    - len -= n;
    + len -= min(len, n);
    written += n;
    }


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