Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 27/63] sysfs: fix use after free in case of concurrent read/write and readdir | Date | Mon, 6 May 2013 15:56:05 -0700 |
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3.4-stable review patch. If anyone has any objections, please let me know.
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From: Ming Lei <ming.lei@canonical.com>
commit f7db5e7660b122142410dcf36ba903c73d473250 upstream.
The inode->i_mutex isn't hold when updating filp->f_pos in read()/write(), so the filp->f_pos might be read as 0 or 1 in readdir() when there is concurrent read()/write() on this same file, then may cause use after free in readdir().
The bug can be reproduced with Li Zefan's test code on the link:
https://patchwork.kernel.org/patch/2160771/
This patch fixes the use after free under this situation.
Reported-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Ming Lei <ming.lei@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/sysfs/dir.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)
--- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -994,6 +994,7 @@ static int sysfs_readdir(struct file * f enum kobj_ns_type type; const void *ns; ino_t ino; + loff_t off; type = sysfs_ns_type(parent_sd); ns = sysfs_info(dentry->d_sb)->ns[type]; @@ -1016,6 +1017,7 @@ static int sysfs_readdir(struct file * f return 0; } mutex_lock(&sysfs_mutex); + off = filp->f_pos; for (pos = sysfs_dir_pos(ns, parent_sd, filp->f_pos, pos); pos; pos = sysfs_dir_next_pos(ns, parent_sd, filp->f_pos, pos)) { @@ -1027,19 +1029,24 @@ static int sysfs_readdir(struct file * f len = strlen(name); ino = pos->s_ino; type = dt_type(pos); - filp->f_pos = pos->s_hash; + off = filp->f_pos = pos->s_hash; filp->private_data = sysfs_get(pos); mutex_unlock(&sysfs_mutex); - ret = filldir(dirent, name, len, filp->f_pos, ino, type); + ret = filldir(dirent, name, len, off, ino, type); mutex_lock(&sysfs_mutex); if (ret < 0) break; } mutex_unlock(&sysfs_mutex); - if ((filp->f_pos > 1) && !pos) { /* EOF */ - filp->f_pos = INT_MAX; + + /* don't reference last entry if its refcount is dropped */ + if (!pos) { filp->private_data = NULL; + + /* EOF and not changed as 0 or 1 in read/write path */ + if (off == filp->f_pos && off > 1) + filp->f_pos = INT_MAX; } return 0; }
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