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authorGuillaume Nault <gnault@redhat.com>2019-02-13 06:30:34 +0300
committerDavid S. Miller <davem@davemloft.net>2019-02-17 05:09:54 +0300
commit4057765f2dee79cb92f9067909477303360be8d3 (patch)
tree26adfd8d86c3e2d0d72f61d78e0d50f6554e9f32 /net/core/sock.c
parentf2281c245d60a8dfe17fada19764d4f7cf1bc4ca (diff)
downloadlinux-4057765f2dee79cb92f9067909477303360be8d3.tar.xz
sock: consistent handling of extreme SO_SNDBUF/SO_RCVBUF values
SO_SNDBUF and SO_RCVBUF (and their *BUFFORCE version) may overflow or underflow their input value. This patch aims at providing explicit handling of these extreme cases, to get a clear behaviour even with values bigger than INT_MAX / 2 or lower than INT_MIN / 2. For simplicity, only SO_SNDBUF and SO_SNDBUFFORCE are described here, but the same explanation and fix apply to SO_RCVBUF and SO_RCVBUFFORCE (with 'SNDBUF' replaced by 'RCVBUF' and 'wmem_max' by 'rmem_max'). Overflow of positive values =========================== When handling SO_SNDBUF or SO_SNDBUFFORCE, if 'val' exceeds INT_MAX / 2, the buffer size is set to its minimum value because 'val * 2' overflows, and max_t() considers that it's smaller than SOCK_MIN_SNDBUF. For SO_SNDBUF, this can only happen with net.core.wmem_max > INT_MAX / 2. SO_SNDBUF and SO_SNDBUFFORCE are actually designed to let users probe for the maximum buffer size by setting an arbitrary large number that gets capped to the maximum allowed/possible size. Having the upper half of the positive integer space to potentially reduce the buffer size to its minimum value defeats this purpose. This patch caps the base value to INT_MAX / 2, so that bigger values don't overflow and keep setting the buffer size to its maximum. Underflow of negative values ============================ For negative numbers, SO_SNDBUF always considers them bigger than net.core.wmem_max, which is bounded by [SOCK_MIN_SNDBUF, INT_MAX]. Therefore such values are set to net.core.wmem_max and we're back to the behaviour of positive integers described above (return maximum buffer size if wmem_max <= INT_MAX / 2, return SOCK_MIN_SNDBUF otherwise). However, SO_SNDBUFFORCE behaves differently. The user value is directly multiplied by two and compared with SOCK_MIN_SNDBUF. If 'val * 2' doesn't underflow or if it underflows to a value smaller than SOCK_MIN_SNDBUF then buffer size is set to its minimum value. Otherwise the buffer size is set to the underflowed value. This patch treats negative values passed to SO_SNDBUFFORCE as null, to prevent underflows. Therefore negative values now always set the buffer size to its minimum value. Even though SO_SNDBUF behaves inconsistently by setting buffer size to the maximum value when passed a negative number, no attempt is made to modify this behaviour. There may exist some programs that rely on using negative numbers to set the maximum buffer size. Avoiding overflows because of extreme net.core.wmem_max values is the most we can do here. Summary of altered behaviours ============================= val : user-space value passed to setsockopt() val_uf : the underflowed value resulting from doubling val when val < INT_MIN / 2 wmem_max : short for net.core.wmem_max val_cap : min(val, wmem_max) min_len : minimal buffer length (that is, SOCK_MIN_SNDBUF) max_len : maximal possible buffer length, regardless of wmem_max (that is, INT_MAX - 1) ^^^^ : altered behaviour SO_SNDBUF: +-------------------------+-------------+------------+----------------+ | CONDITION | OLD RESULT | NEW RESULT | COMMENT | +-------------------------+-------------+------------+----------------+ | val < 0 && | | | No overflow, | | wmem_max <= INT_MAX/2 | wmem_max*2 | wmem_max*2 | keep original | | | | | behaviour | +-------------------------+-------------+------------+----------------+ | val < 0 && | | | Cap wmem_max | | INT_MAX/2 < wmem_max | min_len | max_len | to prevent | | | | ^^^^^^^ | overflow | +-------------------------+-------------+------------+----------------+ | 0 <= val <= min_len/2 | min_len | min_len | Ordinary case | +-------------------------+-------------+------------+----------------+ | min_len/2 < val && | val_cap*2 | val_cap*2 | Ordinary case | | val_cap <= INT_MAX/2 | | | | +-------------------------+-------------+------------+----------------+ | min_len < val && | | | Cap val_cap | | INT_MAX/2 < val_cap | min_len | max_len | again to | | (implies that | | ^^^^^^^ | prevent | | INT_MAX/2 < wmem_max) | | | overflow | +-------------------------+-------------+------------+----------------+ SO_SNDBUFFORCE: +------------------------------+---------+---------+------------------+ | CONDITION | BEFORE | AFTER | COMMENT | | | PATCH | PATCH | | +------------------------------+---------+---------+------------------+ | val < INT_MIN/2 && | min_len | min_len | Underflow with | | val_uf <= min_len | | | no consequence | +------------------------------+---------+---------+------------------+ | val < INT_MIN/2 && | val_uf | min_len | Set val to 0 to | | val_uf > min_len | | ^^^^^^^ | avoid underflow | +------------------------------+---------+---------+------------------+ | INT_MIN/2 <= val < 0 | min_len | min_len | No underflow | +------------------------------+---------+---------+------------------+ | 0 <= val <= min_len/2 | min_len | min_len | Ordinary case | +------------------------------+---------+---------+------------------+ | min_len/2 < val <= INT_MAX/2 | val*2 | val*2 | Ordinary case | +------------------------------+---------+---------+------------------+ | INT_MAX/2 < val | min_len | max_len | Cap val to | | | | ^^^^^^^ | prevent overflow | +------------------------------+---------+---------+------------------+ Signed-off-by: Guillaume Nault <gnault@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core/sock.c')
-rw-r--r--net/core/sock.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/net/core/sock.c b/net/core/sock.c
index d9f0a817dca8..f4b8b78535f8 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -785,6 +785,10 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
*/
val = min_t(u32, val, sysctl_wmem_max);
set_sndbuf:
+ /* Ensure val * 2 fits into an int, to prevent max_t()
+ * from treating it as a negative value.
+ */
+ val = min_t(int, val, INT_MAX / 2);
sk->sk_userlocks |= SOCK_SNDBUF_LOCK;
sk->sk_sndbuf = max_t(int, val * 2, SOCK_MIN_SNDBUF);
/* Wake up sending tasks if we upped the value. */
@@ -796,6 +800,12 @@ set_sndbuf:
ret = -EPERM;
break;
}
+
+ /* No negative values (to prevent underflow, as val will be
+ * multiplied by 2).
+ */
+ if (val < 0)
+ val = 0;
goto set_sndbuf;
case SO_RCVBUF:
@@ -806,6 +816,10 @@ set_sndbuf:
*/
val = min_t(u32, val, sysctl_rmem_max);
set_rcvbuf:
+ /* Ensure val * 2 fits into an int, to prevent max_t()
+ * from treating it as a negative value.
+ */
+ val = min_t(int, val, INT_MAX / 2);
sk->sk_userlocks |= SOCK_RCVBUF_LOCK;
/*
* We double it on the way in to account for
@@ -830,6 +844,12 @@ set_rcvbuf:
ret = -EPERM;
break;
}
+
+ /* No negative values (to prevent underflow, as val will be
+ * multiplied by 2).
+ */
+ if (val < 0)
+ val = 0;
goto set_rcvbuf;
case SO_KEEPALIVE: