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| author | Jiri Slaby <jslaby@suse.cz> | 2016-12-14 15:06:07 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-12-14 16:04:08 -0800 |
| commit | 999898355e08ae3b92dfd0a08db706e0c6703d30 (patch) | |
| tree | 3847a007de4ba475bf867802e20e836ff0d7bf4b /ipc/msg.c | |
| parent | db2aa7fd15e857891cefbada8348c8d938c7a2bc (diff) | |
| download | lwn-999898355e08ae3b92dfd0a08db706e0c6703d30.tar.gz lwn-999898355e08ae3b92dfd0a08db706e0c6703d30.zip | |
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@suse.cz
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc/msg.c')
| -rw-r--r-- | ipc/msg.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/ipc/msg.c b/ipc/msg.c index 32e9bd837cde..e3e52ce01123 100644 --- a/ipc/msg.c +++ b/ipc/msg.c @@ -763,7 +763,10 @@ static inline int convert_mode(long *msgtyp, int msgflg) 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) |