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SubjectRe: [RFC] Coverity 1128444 - Dereference after null check (FORWARD_NULL) in glock.c
From
2013/11/12 Steven Whitehouse <swhiteho@redhat.com>:
> Hi,
>
> On Tue, 2013-11-12 at 12:53 -0200, Geyslan Gregório Bem wrote:
>> Hello,
>>
>> Coverity detected in 'fs/gfs2/glock.c' a possible dereference after
>> null check. Maybe a positive one.
>>
>> There is a initial check for possible 'gl' NULL. After that 'gl' is
>> dereferenced in the looping check by __lockref_is_dead().
>>
>> What do you think?
>>
> I've already been sent a patch for that, and its in the GFS2 -fixes
> tree. Thanks,
>
> Steve.

Steve, thanks.

I'll close it in Coverity.

>
>>
>> 1875static int gfs2_glock_iter_next(struct gfs2_glock_iter *gi)
>> 1876{
>> 1877 struct gfs2_glock *gl;
>> 1878
>> 1879 do {
>> 1880 gl = gi->gl;
>>
>> 1. Condition "gl", taking false branch
>>
>> 2. var_compare_op: Comparing "gl" to null implies that "gl" might be null.
>> 1881 if (gl) {
>> 1882 gi->gl = glock_hash_next(gl);
>> 1883 gi->nhash++;
>> 1884 } else {
>>
>> 3. Condition "gi->hash >= (32768 /* 1 << 15 */)", taking false branch
>> 1885 if (gi->hash >= GFS2_GL_HASH_SIZE) {
>> 1886 rcu_read_unlock();
>> 1887 return 1;
>> 1888 }
>> 1889 gi->gl = glock_hash_chain(gi->hash);
>> 1890 gi->nhash = 0;
>> 1891 }
>>
>> 4. Condition "gi->gl == NULL", taking true branch
>>
>> 7. Condition "gi->gl == NULL", taking false branch
>> 1892 while (gi->gl == NULL) {
>> 1893 gi->hash++;
>>
>> 5. Condition "gi->hash >= (32768 /* 1 << 15 */)", taking false branch
>> 1894 if (gi->hash >= GFS2_GL_HASH_SIZE) {
>> 1895 rcu_read_unlock();
>> 1896 return 1;
>> 1897 }
>> 1898 gi->gl = glock_hash_chain(gi->hash);
>> 1899 gi->nhash = 0;
>>
>> 6. Jumping back to the beginning of the loop
>> 1900 }
>> 1901 /* Skip entries for other sb and dead entries */
>>
>> 8. Condition "gi->sdp != gi->gl->gl_sbd", taking false branch
>>
>> CID 1128444 (#1 of 1): Dereference after null check (FORWARD_NULL)9.
>> var_deref_model: Passing null pointer "&gl->gl_lockref" to function
>> "__lockref_is_dead(struct lockref const *)", which dereferences
>> it.[show details]
>> 1902 } while (gi->sdp != gi->gl->gl_sbd ||
>> __lockref_is_dead(&gl->gl_lockref));
>> 1903
>> 1904 return 0;
>> 1905}
>>
>
>

--
Regards,

Geyslan G. Bem
hackingbits.com
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