Hi All,
as most people know, there are some number of routines in the kernel
that pass back negative error codes as pointers, essentially
doing the cast:
return (void *)-ENOMEM;
These values are supposed to be checked with the routine IS_ERR:
static inline long IS_ERR(const void *ptr)
{
return (unsigned long)ptr > (unsigned long)-1000L;
}
For example:
msg = load_msg(msgp->mtext, msgsz);
if(IS_ERR(msg))
return PTR_ERR(msg);
A bad mistake is to check if such a routine failed by comparing the
result to null. Some code in 2.3.99 did this:
/* ipc/shm.c:750 */
if (!(shp = seg_alloc(...)))
return -ENOMEM;
id = shm_addid(shp);
If seg_alloc did fail, it wouldn't return 0, but instead would give you
back a bogus pointer with lots of high bits set. On some archtectures
using it would let you trash the corresponding chunk of physical memory.
Anyway, we wrote a check to see that IS_ERR functions were handled
consistently. The first pass sees which functions ever get checked using
IS_ERR. The second pass makes sure these always get checked that way.
It didn't find any bugs like the seg_alloc one, but it did find the
opposite case, where code does an IS_ERR check on a function that
actually returns NULL. (A problem, since IS_ERR(0) = 0)
However, these are in namei and reiserfs, so I'm not sure if I'm
misunderstanding some subtle trick.
Dawson
------------------------------------------------------------------------
[BUG] __getname is just kmem_cache_alloc. returns 0 on failure so seems to
cause a segfault.
/u2/engler/mc/oses/linux/2.4.1/fs/namei.c:1930:__vfs_follow_link: NOTE:DERIVE_IS_ERR:EXAMPLE: 'kmem_cache_alloc':1930
name = __getname();
if (IS_ERR(name))
goto fail_name;
strcpy(name, nd->last.name);
nd->last.name = name;
return 0;
------------------------------------------------------------------------
[BUG] grab_cache page returns the result of __grab_cache_page which can
return null. (doesn't seem to return an ERR_PTR)
/u2/engler/mc/oses/linux/2.4.1/fs/reiserfs/inode.c:480:convert_tail_for_hole: NOTE:DERIVE_IS_ERR:EXAMPLE: 'grab_cache_page':480
--------------------------------------------------------------------
[BUG] Ditto: block_prepare_write will deref page.
/u2/engler/mc/oses/linux/2.4.1/fs/reiserfs/inode.c:1490:grab_tail_page: NOTE:DERIVE_IS_ERR:EXAMPLE: 'grab_cache_page':1490
page = grab_cache_page(p_s_inode->i_mapping, index) ;
error = PTR_ERR(page) ;
if (IS_ERR(page)) {
goto out ;
}
/* start within the page of the last block in the file */
start = (offset / blocksize) * blocksize ;
error = block_prepare_write(page, start, offset,
reiserfs_get_block_create_0) ;
--------------------------------------------------------------------
[BUG] Ditto: reiserfs_prepare_write will deref page.
/u2/engler/mc/oses/linux/2.4.1/fs/reiserfs/ioctl.c:81:reiserfs_unpack: NOTE:DERIVE_IS_ERR:EXAMPLE: 'grab_cache_page':81
page = grab_cache_page(inode->i_mapping, index) ;
retval = PTR_ERR(page) ;
if (IS_ERR(page)) {
goto out ;
}
retval = reiserfs_prepare_write(NULL, page, write_from, blocksize) ;
--------------------------------------------------------------------
[BUG]
/u2/engler/mc/oses/linux/2.4.1/fs/buffer.c:1884:block_truncate_page: NOTE:DERIVE_IS_ERR:EXAMPLE: 'grab_cache_page':1884
page = grab_cache_page(mapping, index);
err = PTR_ERR(page);
if (IS_ERR(page))
goto out;
if (!page->buffers)
create_empty_buffers(page, inode->i_dev, blocksize);
------------------------------------------------------------------------
-
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This archive was generated by hypermail 2b29 : Fri Mar 23 2001 - 21:00:16 EST