Messages in this thread Patch in this message |  | | From | Ming Lei <> | | Subject | [PATCH] sysfs: check if one entry has been removed before freeing | | Date | Wed, 3 Apr 2013 10:58:23 +0800 |
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It might be a kernel disaster if one sysfs entry is freed but still referenced by sysfs tree.
Recently Dave and Sasha reported one use-after-free problem on sysfs entry, and the problem has been troubleshooted with help of debug message added in this patch.
Given sysfs_get_dirent/sysfs_put are exported APIs, even inside sysfs they are called in many contexts(kobject/attribe add/delete, inode init/drop, dentry lookup/release, readdir, ...), it is healthful to check the removed flag before freeing one entry and dump message if it is freeing without being removed first.
Cc: Dave Jones <davej@redhat.com> Cc: Sasha Levin <levinsasha928@gmail.com> Signed-off-by: Ming Lei <ming.lei@canonical.com> --- fs/sysfs/dir.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index 1bf016b..328ef9b 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -268,6 +268,13 @@ void release_sysfs_dirent(struct sysfs_dirent * sd) */ parent_sd = sd->s_parent; + if (unlikely(!(sd->s_flags & SYSFS_FLAG_REMOVED))) { + printk(KERN_ERR "sysfs: free using entry: %s/%s\n", + parent_sd ? parent_sd->s_name : "", + sd->s_name); + BUG(); + } + if (sysfs_type(sd) == SYSFS_KOBJ_LINK) sysfs_put(sd->s_symlink.target_sd); if (sysfs_type(sd) & SYSFS_COPY_NAME) @@ -386,7 +393,7 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type) sd->s_name = name; sd->s_mode = mode; - sd->s_flags = type; + sd->s_flags = type | SYSFS_FLAG_REMOVED; return sd; @@ -466,6 +473,9 @@ int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd) ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME; } + /* Mark the entry added into directory tree */ + sd->s_flags &= ~SYSFS_FLAG_REMOVED; + return 0; } -- 1.7.9.5
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