Re: [PATCH v4] ceph: bound encrypted snapshot suffix formatting

[Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>]

On Thu, 2026-04-09 at 10:39 +0800, Pengpeng Hou wrote:
> ceph_encode_encrypted_dname() base64-encodes the encrypted snapshot
> name into the caller buffer and then, for long snapshot names, appends
> _<ino> with sprintf(p + elen, ...).
> 
> Some callers only provide NAME_MAX bytes. For long snapshot names, a
> large inode suffix can push the final encoded name past NAME_MAX even
> though the encrypted prefix stayed within the documented 240-byte
> budget.
> 
> Format the suffix into a small local buffer first and reject names
> whose suffix would exceed the caller's NAME_MAX output buffer.
> 
> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
> ---
> Changes since v3:
> - reject `elen > 240` explicitly instead of relying only on the earlier
>   `WARN_ON()`
> - rewrite the NAME_MAX bound check in terms of the final total length
>   instead of `NAME_MAX - prefix_len - elen`
> 
>  fs/ceph/crypto.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ceph/crypto.c b/fs/ceph/crypto.c
> index f3de43ccb470..42e3fff34697 100644
> --- a/fs/ceph/crypto.c
> +++ b/fs/ceph/crypto.c
> @@ -15,6 +15,12 @@
>  #include "mds_client.h"
>  #include "crypto.h"
>  
> +/*
> + * Reserve room for '_' + decimal 64-bit inode number + trailing NUL.
> + * ceph_encode_encrypted_dname() copies only the visible suffix bytes.
> + */
> +#define CEPH_ENCRYPTED_SNAP_INO_SUFFIX_MAX	sizeof("_18446744073709551615")
> +
>  static int ceph_crypt_get_context(struct inode *inode, void *ctx, size_t len)
>  {
>  	struct ceph_inode_info *ci = ceph_inode(inode);
> @@ -209,6 +215,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
>  	struct inode *dir = parent;
>  	char *p = buf;
>  	u32 len;
> +	int prefix_len = 0;
>  	int name_len = elen;
>  	int ret;
>  	u8 *cryptbuf = NULL;
> @@ -219,6 +226,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
>  		if (IS_ERR(dir))
>  			return PTR_ERR(dir);
>  		p++; /* skip initial '_' */
> +		prefix_len = 1;
>  	}
>  
>  	if (!fscrypt_has_encryption_key(dir))
> @@ -271,8 +279,27 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
>  
>  	/* To understand the 240 limit, see CEPH_NOHASH_NAME_MAX comments */
>  	WARN_ON(elen > 240);
> -	if (dir != parent) // leading _ is already there; append _<inum>
> -		elen += 1 + sprintf(p + elen, "_%ld", dir->i_ino);
> +	if (elen > 240) {
> +		elen = -ENAMETOOLONG;
> +		goto out;
> +	}
> +
> +	if (dir != parent) {
> +		int total_len;
> +		/* leading '_' is already there; append _<inum> */
> +		char suffix[CEPH_ENCRYPTED_SNAP_INO_SUFFIX_MAX];
> +
> +		ret = snprintf(suffix, sizeof(suffix), "_%lu", dir->i_ino);
> +		total_len = prefix_len + elen + ret;
> +		if (total_len > NAME_MAX) {
> +			elen = -ENAMETOOLONG;
> +			goto out;
> +		}
> +
> +		memcpy(p + elen, suffix, ret);
> +		/* Include the leading '_' skipped by p. */
> +		elen = total_len;
> +	}
>  
>  out:
>  	kfree(cryptbuf);

Looks good.

Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>

Let me run xfstests for the patch to double check that everything is OK. I'll
share the result ASAP.

Thanks,
Slava.