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| CodeSonar® 9.0p0 Hot Tips | CONFIDENTIAL | CodeSecure Inc |
An attempt to close a file or socket that has already been closed.
| Class Name | Double Close | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Significance | reliability | ||||||||||||||||||
| Mnemonic | IO.DC | ||||||||||||||||||
| Categories |
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| Availability | Available for C and C++. |
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| Enabling | Checks for this warning class are enabled by
default. To disable them, add the following WARNING_FILTER rule to the
project configuration file.
WARNING_FILTER += discard class="Double Close" |
Calling close() (or a similar function) twice with the same file descriptor can have unexpected negative consequences if the system has recycled the descriptor associated with the closed file:
Japanese (ja)
#include <fcntl.h>
#include <unistd.h>
int double_close(const void *databuf, size_t datasize){
int mydesc;
int yourdesc;
ssize_t s;
int rv;
mydesc = open("myfile.txt", O_CREAT|O_RDONLY);
if (mydesc < 0){return -1;}
close(mydesc);
/* system may recycle the descriptor of the closed file
* giving yourdesc == mydesc */
yourdesc = open("yourfile.txt", O_CREAT|O_RDWR);
if (yourdesc < 0){return -2;}
/* if yourdesc == mydesc, equivalent to close(yourdesc) */
close(mydesc); /* 'Double Close' warning issued here */
/* if yourdesc == mydesc, may fail unexpectedly */
s = write(yourdesc, databuf, datasize);
close(yourdesc);
if (s < 0){return -3;}
return 0;
}
Calling fclose() (or a similar function) twice with the same file pointer causes problems similar to those caused by freeing a pointer twice: undefined and unpredictable behavior including possible memory corruption.
CodeSonar ships with library models that allow it to recognize functions such as libc close() and Win32 FlsFree() that close a file or socket. If one of these functions is called on a file or socket that is already closed, a warning will be issued.
If you have created a custom library model for some function f() in terms of one of these existing models, calls to f() will also be capable of triggering Double Close warnings.
The following configuration file parameters affect checks for this warning class.