The patch titled
Subject: ipc: msg, make msgrcv work with LONG_MIN
has been added to the -mm tree. Its filename is
ipc-msg-make-msgrcv-work-with-long_min.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-msg-make-msgrcv-work-with-long_min.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-msg-make-msgrcv-work-with-long_min.patch
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From: Jiri Slaby <jslaby@xxxxxxx>
Subject: ipc: msg, make msgrcv work with LONG_MIN
When LONG_MIN is passed to msgrcv, one would expect to recieve any
message. But convert_mode does *msgtyp = -*msgtyp and -LONG_MIN is
undefined. In particular, with my gcc -LONG_MIN produces -LONG_MIN again.
So handle this case properly by assigning LONG_MAX to *msgtyp if LONG_MIN
was specified as msgtyp to msgrcv.
This code:
long msg[] = { 100, 200 };
int m = msgget(IPC_PRIVATE, IPC_CREAT | 0644);
msgsnd(m, &msg, sizeof(msg), 0);
msgrcv(m, &msg, sizeof(msg), LONG_MIN, 0);
produces currently nothing:
msgget(IPC_PRIVATE, IPC_CREAT|0644) = 65538
msgsnd(65538, {100, "\310\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16, 0) = 0
msgrcv(65538, ...
Except a UBSAN warning:
UBSAN: Undefined behaviour in ipc/msg.c:745:13
negation of -9223372036854775808 cannot be represented in type 'long int':
With the patch, I see what I expect:
msgget(IPC_PRIVATE, IPC_CREAT|0644) = 0
msgsnd(0, {100, "\310\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16, 0) = 0
msgrcv(0, {100, "\310\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16, -9223372036854775808, 0) = 16
Link: http://lkml.kernel.org/r/20161024082633.10148-1-jslaby@xxxxxxx
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/msg.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff -puN ipc/msg.c~ipc-msg-make-msgrcv-work-with-long_min ipc/msg.c
--- a/ipc/msg.c~ipc-msg-make-msgrcv-work-with-long_min
+++ a/ipc/msg.c
@@ -763,7 +763,10 @@ static inline int convert_mode(long *msg
if (*msgtyp == 0)
return SEARCH_ANY;
if (*msgtyp < 0) {
- *msgtyp = -*msgtyp;
+ if (*msgtyp == LONG_MIN) /* -LONG_MIN is undefined */
+ *msgtyp = LONG_MAX;
+ else
+ *msgtyp = -*msgtyp;
return SEARCH_LESSEQUAL;
}
if (msgflg & MSG_EXCEPT)
_
Patches currently in -mm which might be from jslaby@xxxxxxx are
ipc-msg-make-msgrcv-work-with-long_min.patch
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