Bug 15347 - __FD_MASK triggers undefined behavior
Summary: __FD_MASK triggers undefined behavior
Status: RESOLVED FIXED
Alias: None
Product: glibc
Classification: Unclassified
Component: libc (show other bugs)
Version: 2.19
: P2 normal
Target Milestone: 2.20
Assignee: Florian Weimer
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2013-04-08 13:59 UTC by Florian Weimer
Modified: 2014-06-13 18:28 UTC (History)
1 user (show)

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Last reconfirmed:
fweimer: security-

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Description Florian Weimer 2013-04-08 13:59:53 UTC 
typedef long int __fd_mask;
#define __FD_MASK(d)    ((__fd_mask) 1 << ((d) % __NFDBITS))

1 can be shifted into the sign position, which isn't legal C.

I think we should just use 1UL and cast the result of the shift.
Comment 1 Florian Weimer 2014-02-26 09:13:18 UTC 
Fixed in commit 4cbf380ce948ca15a965a78f0c1a092cf5956792.