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    Subject[PATCH AUTOSEL 5.2 156/171] mm/kmemleak.c: fix check for softirq context
    Date
    From: Dmitry Vyukov <dvyukov@google.com>

    [ Upstream commit 6ef9056952532c3b746de46aa10d45b4d7797bd8 ]

    in_softirq() is a wrong predicate to check if we are in a softirq
    context. It also returns true if we have BH disabled, so objects are
    falsely stamped with "softirq" comm. The correct predicate is
    in_serving_softirq().

    If user does cat from /sys/kernel/debug/kmemleak previously they would
    see this, which is clearly wrong, this is system call context (see the
    comm):

    unreferenced object 0xffff88805bd661c0 (size 64):
    comm "softirq", pid 0, jiffies 4294942959 (age 12.400s)
    hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 ff ff ff ff 00 00 00 00 ................
    00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 ................
    backtrace:
    [<0000000007dcb30c>] kmemleak_alloc_recursive include/linux/kmemleak.h:55 [inline]
    [<0000000007dcb30c>] slab_post_alloc_hook mm/slab.h:439 [inline]
    [<0000000007dcb30c>] slab_alloc mm/slab.c:3326 [inline]
    [<0000000007dcb30c>] kmem_cache_alloc_trace+0x13d/0x280 mm/slab.c:3553
    [<00000000969722b7>] kmalloc include/linux/slab.h:547 [inline]
    [<00000000969722b7>] kzalloc include/linux/slab.h:742 [inline]
    [<00000000969722b7>] ip_mc_add1_src net/ipv4/igmp.c:1961 [inline]
    [<00000000969722b7>] ip_mc_add_src+0x36b/0x400 net/ipv4/igmp.c:2085
    [<00000000a4134b5f>] ip_mc_msfilter+0x22d/0x310 net/ipv4/igmp.c:2475
    [<00000000d20248ad>] do_ip_setsockopt.isra.0+0x19fe/0x1c00 net/ipv4/ip_sockglue.c:957
    [<000000003d367be7>] ip_setsockopt+0x3b/0xb0 net/ipv4/ip_sockglue.c:1246
    [<000000003c7c76af>] udp_setsockopt+0x4e/0x90 net/ipv4/udp.c:2616
    [<000000000c1aeb23>] sock_common_setsockopt+0x3e/0x50 net/core/sock.c:3130
    [<000000000157b92b>] __sys_setsockopt+0x9e/0x120 net/socket.c:2078
    [<00000000a9f3d058>] __do_sys_setsockopt net/socket.c:2089 [inline]
    [<00000000a9f3d058>] __se_sys_setsockopt net/socket.c:2086 [inline]
    [<00000000a9f3d058>] __x64_sys_setsockopt+0x26/0x30 net/socket.c:2086
    [<000000001b8da885>] do_syscall_64+0x7c/0x1a0 arch/x86/entry/common.c:301
    [<00000000ba770c62>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

    now they will see this:

    unreferenced object 0xffff88805413c800 (size 64):
    comm "syz-executor.4", pid 8960, jiffies 4294994003 (age 14.350s)
    hex dump (first 32 bytes):
    00 7a 8a 57 80 88 ff ff e0 00 00 01 00 00 00 00 .z.W............
    00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 ................
    backtrace:
    [<00000000c5d3be64>] kmemleak_alloc_recursive include/linux/kmemleak.h:55 [inline]
    [<00000000c5d3be64>] slab_post_alloc_hook mm/slab.h:439 [inline]
    [<00000000c5d3be64>] slab_alloc mm/slab.c:3326 [inline]
    [<00000000c5d3be64>] kmem_cache_alloc_trace+0x13d/0x280 mm/slab.c:3553
    [<0000000023865be2>] kmalloc include/linux/slab.h:547 [inline]
    [<0000000023865be2>] kzalloc include/linux/slab.h:742 [inline]
    [<0000000023865be2>] ip_mc_add1_src net/ipv4/igmp.c:1961 [inline]
    [<0000000023865be2>] ip_mc_add_src+0x36b/0x400 net/ipv4/igmp.c:2085
    [<000000003029a9d4>] ip_mc_msfilter+0x22d/0x310 net/ipv4/igmp.c:2475
    [<00000000ccd0a87c>] do_ip_setsockopt.isra.0+0x19fe/0x1c00 net/ipv4/ip_sockglue.c:957
    [<00000000a85a3785>] ip_setsockopt+0x3b/0xb0 net/ipv4/ip_sockglue.c:1246
    [<00000000ec13c18d>] udp_setsockopt+0x4e/0x90 net/ipv4/udp.c:2616
    [<0000000052d748e3>] sock_common_setsockopt+0x3e/0x50 net/core/sock.c:3130
    [<00000000512f1014>] __sys_setsockopt+0x9e/0x120 net/socket.c:2078
    [<00000000181758bc>] __do_sys_setsockopt net/socket.c:2089 [inline]
    [<00000000181758bc>] __se_sys_setsockopt net/socket.c:2086 [inline]
    [<00000000181758bc>] __x64_sys_setsockopt+0x26/0x30 net/socket.c:2086
    [<00000000d4b73623>] do_syscall_64+0x7c/0x1a0 arch/x86/entry/common.c:301
    [<00000000c1098bec>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

    Link: http://lkml.kernel.org/r/20190517171507.96046-1-dvyukov@gmail.com
    Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
    Acked-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    mm/kmemleak.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/mm/kmemleak.c b/mm/kmemleak.c
    index 9dd581d11565..3e147ea83182 100644
    --- a/mm/kmemleak.c
    +++ b/mm/kmemleak.c
    @@ -575,7 +575,7 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
    if (in_irq()) {
    object->pid = 0;
    strncpy(object->comm, "hardirq", sizeof(object->comm));
    - } else if (in_softirq()) {
    + } else if (in_serving_softirq()) {
    object->pid = 0;
    strncpy(object->comm, "softirq", sizeof(object->comm));
    } else {
    --
    2.20.1
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