nfsd: make nfs4xdr WRITEMEM safe against zero count
Subsystems (2)
RFC 1/1 nfsd: make nfs4xdr WRITEMEM safe against zero count
WRITEMEM zeroes the last word in the destination buffer for padding purposes, but this must not be done if no bytes are to be copied, as it would result in zeroing of the word right before the array.
--
The current implementation works since it's always called with non zero nbytes or it follows an encoding of the string (or opaque) length which, if equal to zero, can be overwritten with zero.
Another way of implementing that is the way it's done in fs/nfsd/nfs4callback.c:
static inline __be32 *xdr_writemem(__be32 *p, const void *ptr, int nbytes)
{
int tmp = XDR_QUADLEN(nbytes);
if (!tmp)
return p;
p[tmp-1] = 0;
memcpy(p, ptr, nbytes);
return p + tmp;
}#define WRITEMEM(ptr,nbytes) do { \
p = xdr_writemem(p, ptr, nbytes); \
} while (0)Also, is there any plan to clean up the xdr encoding definition any time and define a cleaner static inline API?
I'd be happy to take a stab at it and come up with a written and tested proposal.
Benny
git diff --stat -p
fs/nfsd/nfs4xdr.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
fs/nfsd/nfs4xdr.c +1 -1
@@ -1712,7 +1712,7 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp) *p++ =htonl ((u32)((n) >>32 )); \ *p++ =htonl ((u32)(n)); \ } while (0) -#define WRITEMEM (ptr,nbytes) do { \ +#define WRITEMEM (ptr,nbytes) do if (nbytes > 0) { \ *(p + XDR_QUADLEN(nbytes) -1) = 0; \ memcpy(p, ptr, nbytes); \ p += XDR_QUADLEN(nbytes); \
Quoted 27 lines · Benny Halevy
WRITEMEM zeroes the last word in the destination buffer for padding purposes, but this must not be done if no bytes are to be copied, as it would result in zeroing of the word right before the array.
Signed-off-by Benny Halevy <[email protected]>--
The current implementation works since it's always called with non zero nbytes or it follows an encoding of the string (or opaque) length which, if equal to zero, can be overwritten with zero.Another way of implementing that is the way it's done in
fs/nfsd/nfs4callback.c:static inline
__be32*xdr_writemem(__be32 *p, const void *ptr, int nbytes){ int tmp = XDR_QUADLEN(nbytes); if (!tmp) return p; p[tmp-1] = 0; memcpy(p, ptr, nbytes); return p + tmp; }
Quoted 8 lines
#define WRITEMEM(ptr,nbytes) do { \ p = xdr_writemem(p, ptr, nbytes); \ } while (0)Also, is there any plan to clean up the xdr encoding definition any time and define a cleaner static inline API?
I'd be happy to take a stab at it and come up with a written and tested proposal.
I took a long jump at this last year, but no-one else seemed interested in the work.
Quoted 18 lines
git diff --stat -p
fs/nfsd/nfs4xdr.c| 2 +-1 files changed, 1 insertions(+), 1 deletions(-)fs/nfsd/nfs4xdr.c +1
-1@@ -1712,7 +1712,7 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp) *p++ = htonl((u32)((n) >> 32)); \ *p++ =htonl ((u32)(n)); \ } while (0) -#define WRITEMEM (ptr,nbytes) do { \ +#define WRITEMEM (ptr,nbytes) do if (nbytes > 0) { \ *(p + XDR_QUADLEN(nbytes) -1) = 0; \ memcpy(p, ptr, nbytes); \p += XDR_QUADLEN(nbytes); \
Quoted 4 lines
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--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
Quoted 27 lines · Benny Halevy
WRITEMEM zeroes the last word in the destination buffer for padding purposes, but this must not be done if no bytes are to be copied, as it would result in zeroing of the word right before the array.
Signed-off-by Benny Halevy <[email protected]>--
The current implementation works since it's always called with non zero nbytes or it follows an encoding of the string (or opaque) length which, if equal to zero, can be overwritten with zero.Another way of implementing that is the way it's done in
fs/nfsd/nfs4callback.c:static inline
__be32*xdr_writemem(__be32 *p, const void *ptr, int nbytes){ int tmp = XDR_QUADLEN(nbytes); if (!tmp) return p; p[tmp-1] = 0; memcpy(p, ptr, nbytes); return p + tmp; }
Quoted 8 lines
#define WRITEMEM(ptr,nbytes) do { \ p = xdr_writemem(p, ptr, nbytes); \ } while (0)Also, is there any plan to clean up the xdr encoding definition any time and define a cleaner static inline API?
I'd be happy to take a stab at it and come up with a written and tested proposal.
By the way, here is a pointer to the old work:
http://git.linux-nfs.org/?p=cel/
cel-2.6.git;a=shortlog;h=drop-20070423
The work in this snapshot is only partially complete.
There are many many issues to fix up. One of the bigger ones is that the RPC layer still takes the BKL during XDR encoding and decoding. But I wanted to create something that could be fully or partially shared by the client and server implementations, and that would be more rigorous about static and dynamic type checking.
In addition, the NFSv4 routines use a new style of managing the RPC buffer that I wanted to adopt for the other in-kernel XDR routines, then convert the RPC client to use only the new style when invoking XDR routines. I never got that far, but I still think it's a reasonable goal.
Quoted 18 lines
git diff --stat -p
fs/nfsd/nfs4xdr.c| 2 +-1 files changed, 1 insertions(+), 1 deletions(-)fs/nfsd/nfs4xdr.c +1
-1@@ -1712,7 +1712,7 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp) *p++ = htonl((u32)((n) >> 32)); \ *p++ =htonl ((u32)(n)); \ } while (0) -#define WRITEMEM (ptr,nbytes) do { \ +#define WRITEMEM (ptr,nbytes) do if (nbytes > 0) { \ *(p + XDR_QUADLEN(nbytes) -1) = 0; \ memcpy(p, ptr, nbytes); \p += XDR_QUADLEN(nbytes); \
Quoted 4 lines
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Chuck Lever
chuck[dot]lever[at]oracle[dot]com
Quoted 12 lines · Chuck Lever
By the way, here is a pointer to the old work:
http://git.linux-nfs.org/?p=cel/cel-2.6.git;a=shortlog;h=drop-20070423
The work in this snapshot is only partially complete.
There are many many issues to fix up. One of the bigger ones is that the RPC layer still takes the BKL during XDR encoding and decoding. But I wanted to create something that could be fully or partially shared by the client and server implementations, and that would be more rigorous about static and dynamic type checking.
Quoted 5 lines
In addition, the NFSv4 routines use a new style of managing the RPC buffer that I wanted to adopt for the other in-kernel XDR routines, then convert the RPC client to use only the new style when invoking XDR routines. I never got that far, but I still think it's a reasonable goal.
To find something manageable to start with, what's the minimum first step that that would achieve Benny's goal of replacing those server-side xdr macros?
Quoted 1 line
From a quick glance at the patches: a kerneldoc comment for each xdr
encode/decode seems like overkill, since it's mostly boilerplate; could we document those arguments just once with the definition of kxdrproc_t, then refer to that comment as necessary?
Anyway, seems like good stuff to me.
--b.
Quoted 19 lines · J. Bruce Fields
Quoted 12 lines · Chuck Lever
By the way, here is a pointer to the old work:
http://git.linux-nfs.org/?p=cel/cel-2.6.git;a=shortlog;h=drop-20070423
The work in this snapshot is only partially complete.
There are many many issues to fix up. One of the bigger ones is that the RPC layer still takes the BKL during XDR encoding and decoding. But I wanted to create something that could be fully or partially shared by the client and server implementations, and that would be more rigorous about static and dynamic type checking.
Quoted 5 lines
In addition, the NFSv4 routines use a new style of managing the RPC buffer that I wanted to adopt for the other in-kernel XDR routines, then convert the RPC client to use only the new style when invoking XDR routines. I never got that far, but I still think it's a reasonable goal.
Quoted 3 lines
To find something manageable to start with, what's the minimum first step that that would achieve Benny's goal of replacing those server-side xdr macros?
If we're going to do this, I think we want to replace the macros in both the server and the client.
Thus you want to have a set of shared static inline functions that manage static type checking, data conversion, and bounds checking for basic XDR data types. There are a short series of patches near the beginning of that branch that introduce these helpers. Look at 06e537f7 through cf1ba5ab.
The last one adds generic warning messages on XDR encode and decode errors. We can certainly remove (or provide a kernel config switch for) the decode warnings as they could cause a DoS, but the encode error messages might be useful, and would allow us to remove many of the ad hoc printk's from the XDR functions themselves, resulting in smaller code.
Then, 986ac05e defines the set of NFSv4 XDR data types laid out in RFC3530. The following patches start to fix up the client-side encoders; I didn't get to the client-side decoders, or to the server.
The real effort is going to be reworking the encoders and decoders for the big NFSv4 datatypes, like for instance the arguments and results that contain attributes.
Quoted 4 lines
From a quick glance at the patches: a kerneldoc comment for each xdr encode/decode seems like overkill, since it's mostly boilerplate; could we document those arguments just once with the definition of
kxdrproc_t, then refer to that comment as necessary?
A lot of the changes in that drop are excessive; it was a prototype, so I used the comments to keep track of where I was heading. However, in general I think it's important to document the assumptions relating to the arguments, and the possible return values, for each public function.
Many of the comments in these patches also copy the definition of the XDR data type from the RFC, and call out the RFC section where it is specified. This provides a clear connection between the implementation and the spec to allow easier code review and maintenance.
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
J. Bruce Fields
AppliedQuoted 4 lines · Benny Halevy
WRITEMEM zeroes the last word in the destination buffer for padding purposes, but this must not be done if no bytes are to be copied, as it would result in zeroing of the word right before the array.
Thanks, applied.
Quoted 8 lines
Signed-off-by Benny Halevy <[email protected]>--
The current implementation works since it's always called with non zero nbytes or it follows an encoding of the string (or opaque) length which, if equal to zero, can be overwritten with zero.
I also added the above paragraph to the changelog.
Quoted 15 lines
Another way of implementing that is the way it's done in
fs/nfsd/nfs4callback.c:static inline
__be32*xdr_writemem(__be32 *p, const void *ptr, int nbytes){ int tmp = XDR_QUADLEN(nbytes); if (!tmp) return p; p[tmp-1] = 0; memcpy(p, ptr, nbytes); return p + tmp; }
Quoted 6 lines
#define WRITEMEM(ptr,nbytes) do { \ p = xdr_writemem(p, ptr, nbytes); \ } while (0)Also, is there any plan to clean up the xdr encoding definition any time and define a cleaner static inline API?
Not currently.
Quoted 2 lines
I'd be happy to take a stab at it and come up with a written and tested proposal.
That could be helpful, thanks.
--b.
Quoted 24 lines
Benny
git diff --stat -p
fs/nfsd/nfs4xdr.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)fs/nfsd/nfs4xdr.c +1
-2@@ -1712,7 +1712,7 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp) *p++ =htonl ((u32)((n) >>32 )); \ *p++ =htonl ((u32)(n)); \ } while (0) -#define WRITEMEM (ptr,nbytes) do { \ +#define WRITEMEM (ptr,nbytes) do if (nbytes > 0) { \ *(p + XDR_QUADLEN(nbytes) -1) = 0; \ memcpy(p, ptr, nbytes); \ p += XDR_QUADLEN(nbytes); \ --To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to [email protected]
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