sysfs: check if one entry has been removed before freeing
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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1 changed files with 8 additions and 1 deletions
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@ -268,6 +268,10 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
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*/
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*/
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parent_sd = sd->s_parent;
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parent_sd = sd->s_parent;
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WARN(!(sd->s_flags & SYSFS_FLAG_REMOVED),
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"sysfs: free using entry: %s/%s\n",
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parent_sd ? parent_sd->s_name : "", sd->s_name);
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if (sysfs_type(sd) == SYSFS_KOBJ_LINK)
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if (sysfs_type(sd) == SYSFS_KOBJ_LINK)
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sysfs_put(sd->s_symlink.target_sd);
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sysfs_put(sd->s_symlink.target_sd);
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if (sysfs_type(sd) & SYSFS_COPY_NAME)
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if (sysfs_type(sd) & SYSFS_COPY_NAME)
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@ -386,7 +390,7 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
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sd->s_name = name;
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sd->s_name = name;
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sd->s_mode = mode;
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sd->s_mode = mode;
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sd->s_flags = type;
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sd->s_flags = type | SYSFS_FLAG_REMOVED;
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return sd;
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return sd;
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@ -466,6 +470,9 @@ int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
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ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
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ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
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}
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}
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/* Mark the entry added into directory tree */
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sd->s_flags &= ~SYSFS_FLAG_REMOVED;
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return 0;
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return 0;
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}
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}
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