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    Subject[PATCH v9 08/17] fs: dcache: manually unpoison dname after allocation to shut up kasan's reports
    Date
    We need to manually unpoison rounded up allocation size for dname
    to avoid kasan's reports in dentry_string_cmp().
    When CONFIG_DCACHE_WORD_ACCESS=y dentry_string_cmp may access
    few bytes beyound requested in kmalloc() size.

    dentry_string_cmp() relates on that fact that dentry allocated
    using kmalloc and kmalloc internally round up allocation size.
    So this is not a bug, but this makes kasan to complain about
    such accesses.
    To avoid such reports we mark rounded up allocation size in
    shadow as accessible.

    Reported-by: Dmitry Vyukov <dvyukov@google.com>
    Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
    ---
    fs/dcache.c | 5 +++++
    1 file changed, 5 insertions(+)

    diff --git a/fs/dcache.c b/fs/dcache.c
    index e368d4f..3c097f9 100644
    --- a/fs/dcache.c
    +++ b/fs/dcache.c
    @@ -38,6 +38,8 @@
    #include <linux/prefetch.h>
    #include <linux/ratelimit.h>
    #include <linux/list_lru.h>
    +#include <linux/kasan.h>
    +
    #include "internal.h"
    #include "mount.h"

    @@ -1430,6 +1432,9 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
    }
    atomic_set(&p->u.count, 1);
    dname = p->name;
    + if (IS_ENABLED(CONFIG_DCACHE_WORD_ACCESS))
    + kasan_unpoison_shadow(dname,
    + round_up(name->len + 1, sizeof(unsigned long)));
    } else {
    dname = dentry->d_iname;
    }
    --
    2.2.1


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