Eric Lee / smarc-ti-linux-kernel

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Commit 7904ac84244b59f536c2a5d1066a10f46df07b08

Authored by Earl Chew
Committed by Linus Torvalds
1 parent dc716e96f5
Exists in master and in 20 other branches dlt-processor-sdk-linux-03.00.00.04, newt-ti-linux-3.12.y, processor-sdk-linux-01.00.00, processor-sdk-linux-02.00.01, smarc-ti-linux-3.12.10, smarc-ti-linux-3.12.y, smarc-ti-linux-3.14.y, smarc-ti-linux-3.15.y, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04, ti-linux-3.12.y, ti-linux-3.14.y, ti-linux-3.15.y, ti-lsk-linux-4.1.y

seq_file: fix mishandling of consecutive pread() invocations. 

The following program illustrates the problem:

    char buf[8192];

    int fd = open("/proc/self/maps", O_RDONLY);

    n = pread(fd, buf, sizeof(buf), 0);
    printf("%d\n", n);

    /* lseek(fd, 0, SEEK_CUR); */ /* Uncomment to work around */

    n = pread(fd, buf, sizeof(buf), 0);
    printf("%d\n", n);

The second printf() prints zero, but uncommenting the lseek() corrects its
behaviour.

To fix, make seq_read() mirror seq_lseek() when processing changes in
*ppos.  Restore m->version first, then if required traverse and update
read_pos on success.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=11856

Signed-off-by: Earl Chew <echew@ixiacom.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 1 changed file with 15 additions and 13 deletions Side-by-side Diff

... ... @@ -140,9 +140,21 @@
140 140  
141 141 mutex_lock(&m->lock);
142 142  
  143 + /*
  144 + * seq_file->op->..m_start/m_stop/m_next may do special actions
  145 + * or optimisations based on the file->f_version, so we want to
  146 + * pass the file->f_version to those methods.
  147 + *
  148 + * seq_file->version is just copy of f_version, and seq_file
  149 + * methods can treat it simply as file version.
  150 + * It is copied in first and copied out after all operations.
  151 + * It is convenient to have it as part of structure to avoid the
  152 + * need of passing another argument to all the seq_file methods.
  153 + */
  154 + m->version = file->f_version;
  155 +
143 156 /* Don't assume *ppos is where we left it */
144 157 if (unlikely(*ppos != m->read_pos)) {
145   - m->read_pos = *ppos;
146 158 while ((err = traverse(m, *ppos)) == -EAGAIN)
147 159 ;
148 160 if (err) {
149 161  
... ... @@ -152,21 +164,11 @@
152 164 m->index = 0;
153 165 m->count = 0;
154 166 goto Done;
  167 + } else {
  168 + m->read_pos = *ppos;
155 169 }
156 170 }
157 171  
158   - /*
159   - * seq_file->op->..m_start/m_stop/m_next may do special actions
160   - * or optimisations based on the file->f_version, so we want to
161   - * pass the file->f_version to those methods.
162   - *
163   - * seq_file->version is just copy of f_version, and seq_file
164   - * methods can treat it simply as file version.
165   - * It is copied in first and copied out after all operations.
166   - * It is convenient to have it as part of structure to avoid the
167   - * need of passing another argument to all the seq_file methods.
168   - */
169   - m->version = file->f_version;
170 172 /* grab buffer if we didn't have one */
171 173 if (!m->buf) {
172 174 m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);