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The following root - owned Set - UID program needs to write to a file, but it wants to ensure that the file is owned
The following rootowned SetUID program needs to write to a file, but it wants to
ensure that the file is owned by the user. It uses stat to get the file owners ID
and compares it with the real user ID of the process. If they do not match, the program
will exit. Please describe whether there is a race condition in the program? If so please
explain how you can exploit the race condition. The manual of stat can be found
online.
#include
#include
#include
#include
int main
struct stat statbuf;
uidt realuid;
FILE fp;
fp fopentmpXYZa;
stattmpXYZ &statbuf;
printfThe file owners user ID: d
statbuf.stuid;
printfThe processs real user ID: d
getuid;
Check whether the file belongs to the user
if statbufstuid getuid
printfIDs match, continue to write to the file.
;
write to the file
if fp fclosefp;
else
printfIDs do not match, exit.
;
if fp fclosefp;
return ;
return ;
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