Re: [bug report] fs: fat: create correct short names

26 Jul 2023


      On 26.07.23 09:02, Dan Carpenter wrote:
...
Hello Heinrich Schuchardt,
The patch 28cef9ca2e86: "fs: fat: create correct short names" from
Nov 20, 2020, leads to the following Smatch static
checker warning:
 fs/fat/fat_write.c:61 str2fat()
 warn: impossible condition '(c > 127) => ((-128)-127 > 127)'

 fs/fat/fat_write.c:136 set_name()
 warn: impossible condition '(*dirent.name == 229) => ((-128)-127 == 229)'


fs/fat/fat_write.c
     105 static int set_name(fat_itr *itr, const char *filename, char *shortname)
     106 {
     107         char *period;
     108         char *pos;
     109         int period_location;
     110         char buf[13];
     111         int i;
     112         int ret;
     113         struct nameext dirent;
     114
     115         if (!filename)
     116                 return -EIO;
     117
     118         /* Initialize buffer */
     119         memset(&dirent, ' ', sizeof(dirent));
     120
     121         /* Convert filename to upper case short name */
     122         period = strrchr(filename, '.');
     123         pos = (char *)filename;
     124         if (*pos == '.') {
     125                 pos = period + 1;
     126                 period = 0;
     127         }
     128         if (period)
     129                 str2fat(dirent.ext, period + 1, sizeof(dirent.ext));
     130         period_location = str2fat(dirent.name, pos, sizeof(dirent.name));
     131         if (period_location < 0)
     132                 return period_location;
     133         if (*dirent.name == ' ')
     134                 *dirent.name = '_';
     135         /* 0xe5 signals a deleted directory entry. Replace it by 0x05. */
--> 136         if (*dirent.name == 0xe5)
dirent.name is a char type.  Chars are signed on probably most people's
systems.  The Linux kernel recently made char unsigned for everyone.
Anyway in a char 0xe5 is negative but as a literal, it's positive so
this condition cannot be true.
 137                 *dirent.name = 0x05;

Thanks for reporting the issue. In the same file we have:
fs/fat/fat_write.c:1493:
         dent->nameext.name[0] = DELETED_FLAG;
include/fat.h:53:
#define DELETED_FLAG   ((char)0xe5)
I will send a patch.
Best regards
Heinrich
...
 138
 139         /* If filename and short name are the same, quit. */
 140         sprintf(buf, "%.*s.%.3s", period_location, dirent.name, dirent.ext);
 141         if (!strcmp(buf, filename)) {
 142                 ret = 1;


regards,
dan carpenter