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GFS2: don't set rgrp gl_object until it's inserted into rgrp tree 

Before this patch, function read_rindex_entry would set a rgrp
glock's gl_object pointer to itself before inserting the rgrp into
the rgrp rbtree. The problem is: if another process was also reading
the rgrp in, and had already inserted its newly created rgrp, then
the second call to read_rindex_entry would overwrite that value,
then return a bad return code to the caller. Later, other functions
would reference the now-freed rgrp memory by way of gl_object.
In some cases, that could result in gfs2_rgrp_brelse being called
twice for the same rgrp: once for the failed attempt and once for
the "real" rgrp release. Eventually the kernel would panic.
There are also a number of other things that could go wrong when
a kernel module is accessing freed storage. For example, this could
result in rgrp corruption because the fake rgrp would point to a
fake bitmap in memory too, causing gfs2_inplace_reserve to search
some random memory for free blocks, and find some, since we were
never setting rgd->rd_bits to NULL before freeing it.

This patch fixes the problem by not setting gl_object until we
have successfully inserted the rgrp into the rbtree. Also, it sets
rd_bits to NULL as it frees them, which will ensure any accidental
access to the wrong rgrp will result in a kernel panic rather than
file system corruption, which is preferred.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
This commit is contained in:
Bob Peterson 2016-06-09 14:24:07 -05:00
parent 29567292c0
commit 36e4ad0316
1 changed files with 8 additions and 4 deletions
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12
fs/gfs2/rgrp.c
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@ -722,6 +722,7 @@ void gfs2_clear_rgrpd(struct gfs2_sbd *sdp)
gfs2_free_clones(rgd);
kfree(rgd->rd_bits);
rgd->rd_bits = NULL;
return_all_reservations(rgd);
kmem_cache_free(gfs2_rgrpd_cachep, rgd);
}
@ -916,9 +917,6 @@ static int read_rindex_entry(struct gfs2_inode *ip)
if (error)
goto fail;
rgd->rd_gl->gl_object = rgd;
rgd->rd_gl->gl_vm.start = (rgd->rd_addr * bsize) & PAGE_MASK;
rgd->rd_gl->gl_vm.end = PAGE_ALIGN((rgd->rd_addr + rgd->rd_length) * bsize) - 1;
rgd->rd_rgl = (struct gfs2_rgrp_lvb *)rgd->rd_gl->gl_lksb.sb_lvbptr;
rgd->rd_flags &= ~(GFS2_RDF_UPTODATE | GFS2_RDF_PREFERRED);
if (rgd->rd_data > sdp->sd_max_rg_data)
@ -926,14 +924,20 @@ static int read_rindex_entry(struct gfs2_inode *ip)
spin_lock(&sdp->sd_rindex_spin);
error = rgd_insert(rgd);
spin_unlock(&sdp->sd_rindex_spin);
if (!error)
if (!error) {
rgd->rd_gl->gl_object = rgd;
rgd->rd_gl->gl_vm.start = (rgd->rd_addr * bsize) & PAGE_MASK;
rgd->rd_gl->gl_vm.end = PAGE_ALIGN((rgd->rd_addr +
rgd->rd_length) * bsize) - 1;
return 0;
}
error = 0; /* someone else read in the rgrp; free it and ignore it */
gfs2_glock_put(rgd->rd_gl);
fail:
kfree(rgd->rd_bits);
rgd->rd_bits = NULL;
kmem_cache_free(gfs2_rgrpd_cachep, rgd);
return error;
}