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    Subject[PATCH 4.19 014/134] net: rose: fix a possible stack overflow
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit e5dcc0c3223c45c94100f05f28d8ef814db3d82c ]

    rose_write_internal() uses a temp buffer of 100 bytes, but a manual
    inspection showed that given arbitrary input, rose_create_facilities()
    can fill up to 110 bytes.

    Lets use a tailroom of 256 bytes for peace of mind, and remove
    the bounce buffer : we can simply allocate a big enough skb
    and adjust its length as needed.

    syzbot report :

    BUG: KASAN: stack-out-of-bounds in memcpy include/linux/string.h:352 [inline]
    BUG: KASAN: stack-out-of-bounds in rose_create_facilities net/rose/rose_subr.c:521 [inline]
    BUG: KASAN: stack-out-of-bounds in rose_write_internal+0x597/0x15d0 net/rose/rose_subr.c:116
    Write of size 7 at addr ffff88808b1ffbef by task syz-executor.0/24854

    CPU: 0 PID: 24854 Comm: syz-executor.0 Not tainted 5.0.0+ #97
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    Call Trace:
    __dump_stack lib/dump_stack.c:77 [inline]
    dump_stack+0x172/0x1f0 lib/dump_stack.c:113
    print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
    kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
    check_memory_region_inline mm/kasan/generic.c:185 [inline]
    check_memory_region+0x123/0x190 mm/kasan/generic.c:191
    memcpy+0x38/0x50 mm/kasan/common.c:131
    memcpy include/linux/string.h:352 [inline]
    rose_create_facilities net/rose/rose_subr.c:521 [inline]
    rose_write_internal+0x597/0x15d0 net/rose/rose_subr.c:116
    rose_connect+0x7cb/0x1510 net/rose/af_rose.c:826
    __sys_connect+0x266/0x330 net/socket.c:1685
    __do_sys_connect net/socket.c:1696 [inline]
    __se_sys_connect net/socket.c:1693 [inline]
    __x64_sys_connect+0x73/0xb0 net/socket.c:1693
    do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
    entry_SYSCALL_64_after_hwframe+0x49/0xbe
    RIP: 0033:0x458079
    Code: ad b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
    RSP: 002b:00007f47b8d9dc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
    RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458079
    RDX: 000000000000001c RSI: 0000000020000040 RDI: 0000000000000004
    RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000246 R12: 00007f47b8d9e6d4
    R13: 00000000004be4a4 R14: 00000000004ceca8 R15: 00000000ffffffff

    The buggy address belongs to the page:
    page:ffffea00022c7fc0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
    flags: 0x1fffc0000000000()
    raw: 01fffc0000000000 0000000000000000 ffffffff022c0101 0000000000000000
    raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
    page dumped because: kasan: bad access detected

    Memory state around the buggy address:
    ffff88808b1ffa80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ffff88808b1ffb00: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 00 03
    >ffff88808b1ffb80: f2 f2 00 00 00 00 00 00 00 00 00 00 00 00 04 f3
    ^
    ffff88808b1ffc00: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
    ffff88808b1ffc80: 00 00 00 00 00 00 00 f1 f1 f1 f1 f1 f1 01 f2 01

    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/rose/rose_subr.c | 21 ++++++++++++---------
    1 file changed, 12 insertions(+), 9 deletions(-)

    --- a/net/rose/rose_subr.c
    +++ b/net/rose/rose_subr.c
    @@ -105,16 +105,17 @@ void rose_write_internal(struct sock *sk
    struct sk_buff *skb;
    unsigned char *dptr;
    unsigned char lci1, lci2;
    - char buffer[100];
    - int len, faclen = 0;
    + int maxfaclen = 0;
    + int len, faclen;
    + int reserve;

    - len = AX25_BPQ_HEADER_LEN + AX25_MAX_HEADER_LEN + ROSE_MIN_LEN + 1;
    + reserve = AX25_BPQ_HEADER_LEN + AX25_MAX_HEADER_LEN + 1;
    + len = ROSE_MIN_LEN;

    switch (frametype) {
    case ROSE_CALL_REQUEST:
    len += 1 + ROSE_ADDR_LEN + ROSE_ADDR_LEN;
    - faclen = rose_create_facilities(buffer, rose);
    - len += faclen;
    + maxfaclen = 256;
    break;
    case ROSE_CALL_ACCEPTED:
    case ROSE_CLEAR_REQUEST:
    @@ -123,15 +124,16 @@ void rose_write_internal(struct sock *sk
    break;
    }

    - if ((skb = alloc_skb(len, GFP_ATOMIC)) == NULL)
    + skb = alloc_skb(reserve + len + maxfaclen, GFP_ATOMIC);
    + if (!skb)
    return;

    /*
    * Space for AX.25 header and PID.
    */
    - skb_reserve(skb, AX25_BPQ_HEADER_LEN + AX25_MAX_HEADER_LEN + 1);
    + skb_reserve(skb, reserve);

    - dptr = skb_put(skb, skb_tailroom(skb));
    + dptr = skb_put(skb, len);

    lci1 = (rose->lci >> 8) & 0x0F;
    lci2 = (rose->lci >> 0) & 0xFF;
    @@ -146,7 +148,8 @@ void rose_write_internal(struct sock *sk
    dptr += ROSE_ADDR_LEN;
    memcpy(dptr, &rose->source_addr, ROSE_ADDR_LEN);
    dptr += ROSE_ADDR_LEN;
    - memcpy(dptr, buffer, faclen);
    + faclen = rose_create_facilities(dptr, rose);
    + skb_put(skb, faclen);
    dptr += faclen;
    break;


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