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dccp: allow probing of CCID-array length 

This fixes a problem in the DCCP getsockopt() API: currently there is no way
for a user to a priori know the number of built-in CCIDs, other than trying
DCCP_SOCKOPT_AVAILABLE_CCIDS in a loop, incrementing the option length until
EINVAL is no longer returned.

This patch truncates the array to the user-provided length. No copy is made
when the length is <= 0.

Due to the length restriction in do_dccp_getsockopt() to sizeof(int), the
minimum array length remains 4, which is a reasonable default (only 3
CCIDs, CCID-2..4, are currently defined).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gerrit Renker 2010-02-07 20:20:28 +00:00 committed by David S. Miller
parent 7455a76f17
commit 69a6a0b38a
2 changed files with 8 additions and 7 deletions
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6
Documentation/networking/dccp.txt
View File

@ -58,8 +58,10 @@ DCCP_SOCKOPT_GET_CUR_MPS is read-only and retrieves the current maximum packet
size (application payload size) in bytes, see RFC 4340, section 14.
DCCP_SOCKOPT_AVAILABLE_CCIDS is also read-only and returns the list of CCIDs
supported by the endpoint (see include/linux/dccp.h for symbolic constants).
The caller needs to provide a sufficiently large (> 2) array of type uint8_t.
supported by the endpoint. The option value is an array of type uint8_t whose
size is passed as option length. The minimum array size is 4 elements, the
value returned in the optlen argument always reflects the true number of
built-in CCIDs.
DCCP_SOCKOPT_CCID is write-only and sets both the TX and RX CCIDs at the same
time, combining the operation of the next two socket options. This option is

9
net/dccp/ccid.c
View File

@ -63,14 +63,13 @@ int ccid_getsockopt_builtin_ccids(struct sock *sk, int len,
u8 *ccid_array, array_len;
int err = 0;
if (len < ARRAY_SIZE(ccids))
return -EINVAL;
if (ccid_get_builtin_ccids(&ccid_array, &array_len))
return -ENOBUFS;
if (put_user(array_len, optlen) ||
copy_to_user(optval, ccid_array, array_len))
if (put_user(array_len, optlen))
err = -EFAULT;
else if (len > 0 && copy_to_user(optval, ccid_array,
len > array_len ? array_len : len))
err = -EFAULT;
kfree(ccid_array);