3.16.74-rc1 review patch. If anyone has any objections, please let me know.
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From: Bob Peterson rpeterso@redhat.com
commit 36e4ad0316c017d5b271378ed9a1c9a4b77fab5f upstream.
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 [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/fs/gfs2/rgrp.c +++ b/fs/gfs2/rgrp.c @@ -731,6 +731,7 @@ void gfs2_clear_rgrpd(struct gfs2_sbd *s
gfs2_free_clones(rgd); kfree(rgd->rd_bits); + rgd->rd_bits = NULL; return_all_reservations(rgd); kmem_cache_free(gfs2_rgrpd_cachep, rgd); } @@ -925,10 +926,6 @@ static int read_rindex_entry(struct gfs2 if (error) goto fail;
- rgd->rd_gl->gl_object = rgd; - rgd->rd_gl->gl_vm.start = (rgd->rd_addr * bsize) & PAGE_CACHE_MASK; - rgd->rd_gl->gl_vm.end = PAGE_CACHE_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; if (rgd->rd_data > sdp->sd_max_rg_data) @@ -936,14 +933,20 @@ static int read_rindex_entry(struct gfs2 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; }