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

[Viacheslav Dubeyko]

On Thu, 2026-04-09 at 18:09 +0000, Viacheslav Dubeyko wrote:
> 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@xxxxxxxxxxx>
> > ---
> > 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@xxxxxxx>
> 
> Let me run xfstests for the patch to double check that everything is OK. I'll
> share the result ASAP.
> 

The xfstests run was successful. I don't see any issues with the patch.

Tested-by: Viacheslav Dubeyko <Slava.Dubeyko@xxxxxxx>

Thanks,
Slava.