Re: [PATCH 01/13] sysfs: Update sysfs_setxattr so it updates secdata under the sysfs_mutex

Serge E. Hallyn
2009-11-03T13:48:43Z

Quoting Eric W. Biederman (ebiederm@xmission.com):
> From: Eric W. Biederman <ebiederm@aristanetworks.com>
>
> The sysfs_mutex is required to ensure updates are and will remain
> atomic with respect to other inode iattr updates, that do not happen
> through the filesystem.
>
> Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
> ---
> fs/sysfs/inode.c | 41 +++++++++++++++++++++++++++++------------
> 1 files changed, 29 insertions(+), 12 deletions(-)
>
> diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
> index e28cecf..8a08250 100644
> --- a/fs/sysfs/inode.c
> +++ b/fs/sysfs/inode.c
> @@ -122,23 +122,39 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
> return error;
> }
>
> +static int sysfs_sd_setsecdata(struct sysfs_dirent *sd, void **secdata, u32 *secdata_len)
> +{
> + struct sysfs_inode_attrs *iattrs;
> + void *old_secdata;
> + size_t old_secdata_len;
> +
> + iattrs = sd->s_iattr;
> + if (!iattrs)
> + iattrs = sysfs_init_inode_attrs(sd);
> + if (!iattrs)
> + return -ENOMEM;
> +
> + old_secdata = iattrs->ia_secdata;
> + old_secdata_len = iattrs->ia_secdata_len;
> +
> + iattrs->ia_secdata = *secdata;
> + iattrs->ia_secdata_len = *secdata_len;
> +
> + *secdata = old_secdata;
> + *secdata_len = old_secdata_len;
> + return 0;
> +}
> +
> int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> size_t size, int flags)
> {
> struct sysfs_dirent *sd = dentry->d_fsdata;
> - struct sysfs_inode_attrs *iattrs;
> void *secdata;
> int error;
> u32 secdata_len = 0;
>
> if (!sd)
> return -EINVAL;
> - if (!sd->s_iattr)
> - sd->s_iattr = sysfs_init_inode_attrs(sd);
> - if (!sd->s_iattr)
> - return -ENOMEM;
> -
> - iattrs = sd->s_iattr;
>
> if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN)) {
> const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
> @@ -150,12 +166,13 @@ int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> &secdata, &secdata_len);
> if (error)
> goto out;
> - if (iattrs->ia_secdata)
> - security_release_secctx(iattrs->ia_secdata,
> - iattrs->ia_secdata_len);
> - iattrs->ia_secdata = secdata;
> - iattrs->ia_secdata_len = secdata_len;
>
> + mutex_lock(&sysfs_mutex);
> + error = sysfs_sd_setsecdata(sd, &secdata, &secdata_len);

You're ignoring the potential -ENOMEM return value here?

Worse, if -ENOMEM, then secdata was never set, so you call
security_release_secctx() on a random value left on the stack...

> + mutex_unlock(&sysfs_mutex);
> +
> + if (secdata)
> + security_release_secctx(secdata, secdata_len);
> } else
> return -EINVAL;
> out:
> --
> 1.6.5.2.143.g8cc62
>
> --
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