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authorMing Lei <ming.lei@canonical.com>2013-04-02 10:12:26 +0800
committerBen Hutchings <ben@decadent.org.uk>2013-05-13 15:02:13 +0100
commit3a8aad02f417b5aecafdc785c39c0e2259995c69 (patch)
tree956423616bd281c99edbb37912c283cca1d3832f /fs
parent893bee37f931a600f473801ee1c9c3e2030c2c86 (diff)
sysfs: fix use after free in case of concurrent read/write and readdir
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> [bwh: Backported to 3.2: file position is child inode number, not hash] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'fs')
-rw-r--r--fs/sysfs/dir.c15
1 files changed, 11 insertions, 4 deletions
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 3899e240c29..e756bc4d98a 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -977,6 +977,7 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
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];
@@ -999,6 +1000,7 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
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)) {
@@ -1010,19 +1012,24 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
len = strlen(name);
ino = pos->s_ino;
type = dt_type(pos);
- filp->f_pos = ino;
+ off = filp->f_pos = ino;
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;
}